Tbh. Their alibi is hard to buy. They just need to look into their logs and cross check with what info OP has provided. How is it not technically possible?
Tviton: the fault that the customer has lost the funds completely his as
not specifying memo in the cryptocurrency xlm is the same as to send
cryptocurrency to another address
Completely different scenario actually. As long as the coins is sitting in an address they control of (or whatever purse they have), there's a chance to recover it (in this case, manually credit is a more appropriate term) contrary to sent to a wrong address situation where the exchange has absolutely no control nor knows who owns it.
The whole thing is easy to execute. Now they just don't want to return the coins, even when OP provided proof, and have now decided to make excuses. It's just a matter of sending an equivalent number of coins to the complainant's address now that he provided proof, and everyone leaves happy.
