Blockchain wallet actually is too buggy I have experienced before using their wallet that sometimes my balance becomes zero or my funds are gone. I always reported it to support and request to refresh my account to fix the issue. After that, they refresh my account and solved my issue. So if all suggestion above doesn't work only support can help you about this issue.
I suggest you next time don't use any online wallet like blockchain and better switch to Electrum wallet a other suggested above.
Have you saved your recovery phrase (a series of 12 words)?
Using your recovery phrase, you can import your wallet into another wallet like
electrum and access your fund easily.
Is this will work?
I never heard that the 12 words seed from blockchain when you import it to Electrum you will see your funds?
So I think this will not work so the only solution is to report this to the support and send all of his funds to the new wallet in Electrum.