Actually, what Blockchain.com support writes about is that if you yourself did not change the email address to confirm login to your account, but this email address has been changed, it means that someone did it and the wallet is definitely compromised. 
And of course you can’t use it even if you still get access to it.

 In your case, I would try the following course of action.  If you know for sure that it was from your currently working email address that the wallet was registered, then you can continue corresponding with support and invite them to send you an archived backup copy of the Wallet.aes.json file (by the way, if you don’t know the .  aes. means that the file is encrypted in this case with a password that you yourself created during the initial registration of your wallet).
 The Blockchain.com service has a tool for importing Wallet.aes.json using this password, known only to you. (https://login.blockchain.com/wallet/import-wallet)
 After such decryption, you will be able to find out the privatekey of your account.  And accordingly gain access to this account.
 However, it may be difficult to ask support to send you this file.  It really is possible.  Here I don’t know how user-friendly they are.  Their arguments may also be logical and consist in the fact that such sending of the Wallet.aes.json file is also partly a violation of the security protocol.  Due to possible hacking of your email address.
 But still, it is precisely this way of solving the problem that I would move on.

 Here are some more useful links to Blockchain.com documents for communicating with support and for a substantive, reasoned discussion of your rights as a consumer of the services of this service

https://www.blockchain.com/en/legal/terms

https://www.blockchain.com/en/legal/privacy

https://www.blockchain.com/en/learning-portal/how-it-works/


Here is another useful post nc50lc on this topic (Wallet.aes.json)

https://bitcointalk.org/index.php?topic=5303349.msg63278032#msg63278032