They said this ID is linked to an email address which definitely isn't mine (they didn't give me the full address but a couple of letters)
Should I assume that my wallet has been hacked and that the hackers changed the email address?
Yes, that is the reasonable assumption given the situation. Have you checked the email address for any message of a change in email address or an access to the wallet that you did not initiate.
I have no idea what to do now. Do Blockchain have a fraud department?
I have the set up email address and all security info.
Give that information to their support, reporting the account as hacked. If you had any funds on the wallet before, you can consider that lost already.
- Jay -