I made a test transfer to coinbase and saw that address indeed changed after receiving the coins.I believe the earlier transfer changed and disappeared without crediting the account first
I talked to blockchain and believe that they are not at fault.
Coinbase has still not answered the first email and there is no other way to contact them.I believe that this is what happened
Second sent email to coinbase :
Hello i believe coinbase took my bitcoin cash.
I made a transfer of over 10 bitcoin cash to my coinbase wallet, but after sending the coins my coinbase wallet address had changed and there was no history of transfer
The coins are currently in an untouched address which i believe to belong to coinbase and i believe that there was a coinbase wallet mistake and error in my account
Coinbase generate new addresses automatically after every transactions you made. These new addresses are also generated when your funds are moved between your coinbase wallets.
It is done for your security to remain anonymous from third parties.
And I guess those used addresses can also be reused. So your deposits will still arrive on your wallet if you used that.
I already experienced it on other exchanges, but for a withdrawal request, I booked a ticket several times and then it went back to my wallet after a week.
Maybe there are just some errors on your wallet input. Probably you accidentally removed or added characters.
But hope and wait for coinbase to take action.