I bought some USDC and sent them to my Coinomi wallet, but they have never appear on the wallet. I have no way to use them, despite I can still see them on the Etherscan.
Coinomi has quite a few problems. And one of them is the fact that the developers are pretty incompetent.
I hope you can fix your issue somehow. It might be just a connection error, can you confirm that you actually have an active connection and the up-to-date version?
After you gained access, you might want to user a proper open-source wallet, and not a wallet whose developer think its not a severe vulnerability to spell-check your mnemonic code with the use of google.
I'd definitely suggest you to not use coinomi after fixing your issue.