Thank you - both of you for your replies. I will follow up on your suggestions. I am scared now because I still have some Bitcoin stashed in one of their vaults and the only way to get that out is by selling it and withdrawing the cash - so if they decide that they just can't be bothered to do the transfer one is proverbially shafted.
I am just amazed because there seem to be so many people like me having exactly the same problems and their customer service is like the garbage end of a hyaenas bachelor party.
I'm not that familiar with Coinbase's vault features, but is there any way to withdraw the bitcoin directly from Coinbase into another wallet? If so, check out this article:
https://bitcoin.org/en/choose-your-walletOnce you've created a wallet, you may explore other options of getting your money out after you transfer your crypto to your newly created wallet. The best? Look for a trusted reputable bitcoin buyer here to do an exchange for you. You may have to send the bitcoin first, but make sure that the buyer is very reputable.
Don't sell your bitcoin and try to withdraw it from coinbase. Simply withdraw your balance to your own wallet ASAP.