Did you not get a response from Abra customer service yet? Continue to ask help in all their social media channels. They are your best shot.

Someone may take your offer since there's a reward involved but don't entertain just anyone who sends you a private message. Perhaps you can also offer this to Abra CS so they'll expedite your request  

Do not mind them, it is 12. If the first word start with at, just ignore it. Then write the other 12.

When I created the wallet for experiment today, this was the seed phrase generated:

at mention country giant rice boss people bid asset boring midnight wise begin

I know it will be 12, and iamcoleman tool indicated no 'at' in BIP39 seed phrase. Just neglect 'at', if there.

Please, do not share your seed phrase with anyone. This one is used for my research purpose today.

This got me confused too as I told migs360 to get the private key using iamcoleman but said he is unable to do that. If you check my first posts up here, immediately I saw this topic, I generated Abra's wallet and I was given the 12 words seed phrase, I used it offline on iancoleman and it generated me the seed and the extended private key which I believe it can be used. But migs360 is saying another thing which I believe either he has lost his seed phrase or inputting a wrong seed phrase. I believe only using the seed phrase will also work on wallets like Coinomi, he said it did not work too. He needs to truly contact yogg for further assistance.

Do not contact wrong person, make sure you contact him using Bitcointalk PM. This is yogg profile link:

https://bitcointalk.org/index.php?action=profile;u=140827

akirasendo17 & cheezcarls , OP is in possession of his Abra backup (13 words seed) so nothing is lost, he just needs to find a way to get the private key from that address to which the USDT is sent.

migs360, I suggest you contact @yogg, and I'm pretty sure he can help you. This is a specific situation, and members who don't read at all can't help you - as long as you have a seed, I believe you have a great chance of finding a solution.

Go to iamcoleman
https://iancoleman.io/bip39/

Scroll down the tool to see how you can use it offline.

Then, if offline, you will set the seed word from 15 to 12, I believe Abra's wallet generate 12 seed words for you. Or set it the the one you have with you.

Then, input the seed phrase into  BIP39 Mnemonic space provided by the tool. Then the derivation paths will automatically be generated. And scroll down.

The Derivation Path will be BIP44 automatically, which is the derivation part for legacy addresses. If not set to BIP44, then click on BIP44.

Scroll down to copy the Account Extended Private Key.

You can import it on USDt supported wallet, and let us know if it works.

Do not do this online, it is not safe. Do it offline.

That means mk4 is right, then Abra's wallet is not a good wallet, you should make sure to send USDt to the wallets that support the USDt next time, a single mistake can make your coin lost forever.

But, should I tell you how you can extract out your legacy address from thee seed pjhrase to try it if it will work?

I have just created Abras wallet now, it generated me 12 words seed phrase. Which means the tether is not lost and can still be accessed by migs360. All he need is to try out the seed phrase on wallet that supported USDt because Abra's wallet is not supporting USDt.

I confirmed that the seed phrase is BIP39 on iancoleman.io, the tool generated me the root seed, the extenteded private key and the extenteded public key for the seed phrase generated on Abra's wallet.

You do not need to contact Abra's support team because the transaction was successful.

I will not recommend coinomi because it is close source, but in this case, I will advice you to use coinomi for the recovery. Import your Abra's wallet seed phrase on Coinomi, you tether balance will appear. Try that iand tell us if you see the balance. According to your txid, the address start from 1, which means importing your Abra's seed phrase on Coinomi will make your USDt appear on Coinomi, and you can spent it.

How many times you've contacted them? sorry but that mistake, no one can help you into it but only Abra if they truly have a solution for it. Did you reach them with their other contacts?
https://support.abra.com/hc/en-us/articles/216665658-How-can-I-contact-you-

Not sure If you can recovered that. Since usdt is supported by blockchain but too far to be close to bitcoin blockchain. There is tron, binance chain, erc20 and omni but I'm wondering how the process would succeed even with different blockchain used. But indeed it was accepted based on the address it is legacy address of bitcoin you have used. Curious if this will work or abra can managed returning your fund. Hope you could get that amount it's quite big.