Be careful, do not share either of your privatekey or seed phrase to anyone or you will lose all your funds. I am not sure if you can take back what you have sent and as you mentioned you have sent BCH to a BTC address. Better try to contact the wallet's support and see of there is anything that they can do. Again do not share your private key or seed pharase even if you are talking to an admin or support.

The question, did you have the private key, seed phrase of that bitcoin address if you don't have the private key of that bitcoin address then could be gone for your fund.

You should answer the question in the reply above yours and give more details about the transaction for further assistance;
Was it a payment for a service? And was it sent to an individual or a business?
• If it was an individual and you were paying for something, it's most likely a scam attempt and they are lying about not getting it as the funds are already received and spent from the address.

There is also the possibility that the mistake was from your end and you sent the funds to the wrong address.

you can check by yourself if a transaction has been transmitted and has been confirmed
http://blockchair.com/bitcoin/address/3NkWAoSCmxjEGvUnMfv8NXMfaV935z74vA
last receiving transaction has been seen 6 days ago and now it is empty. what is the amount/day that you have sent bitcoin? however it is impossible to reverse the payment or get "bitcoin back".

I don't know if it's just me but both of those addresses don't look to have a balance on blockchair? Can you post the txid and are you sure you sent the transaction? What software were you using?