What can I do if someone obtained control of my blockchain wallet?
To be completely safe, you should throw away every piece of information and data to do with the old wallets used or accessed by the scammer. user-ids, passwords, recovery phrases, backups, keys, addresses and anything else that is related to anything the scammer had access to.
Those wallets and the keys in them are forever unsafe. Even if you reset passwords, change 2FA or do anything else they are still unsafe forever.
In those circumstances I would assume the scammer also has back-door access to any computers or phones or other devices that you, or anyone else in your house owned at the time of the scam.
I would back up any important data (photos, email, other documents) and wipe those devices clean and reinstall the operating systems then sell them.
I would only create a new wallet using reliable sources on a new computer or phone that has never been used on the same local network as any of the devices owned at the time of the scam.
This may seem extreme and it may be unlikely that all of it is necessary in your case. But you don't know for certain. The only way to be sure is to take extreme measures so far as you are able and/or live with the remaining risk.
If you are 100% certain the scammer never persuaded you to install software and never used remote access to share a screen to help you, then your devices might be OK, but you need to be certain.

Postscript:

Typically, potential investors are prompted to fill in an online contact form and then encouraged over the phone to set up a cryptocurrency wallet - but unknown to them the scammer installs remote access software on their device, granting them access to it as well.

From https://www.bbc.co.uk/news/technology-57267199 2021-05-27