4Game

Don't know if it's the right place to post something like this so sorry in advance!
My dad had his account for about 11 years now, but in the last couple of years he doesn't play much (life goes on) so from time to time I would login to make sure everything's good in the account, some time ago when I wanted to check that everything is good and someone was playing on the account, no idea who.
so I changed the password, added a 2-step authenticator and that's about it right ? everything should be "secure".
well, it's not secure, 2 or 3 days ago I logged in to collect the "well deserved awards" for 2022, and noticed some suspicious things (different nickname (there was an option to change for free since we moved from CIS), missing tokens, missing gold, missing bonds, missing tanks, new tank, etc.)
so I contacted Wargaming and they decided to lock the account so no further damage may occur (they did say it got hacked, so much for 2-Step protection right ?), makes sense that they will lock now.
Thing is, now in order to prove that I'm the owner, they want me to provide me the ISP that was used 11 YEARS AGO when the account was created and the city in which the account was created and the associated phone number.
Phone number is easy, it's my dad's phone, but how the hell am I suppose to remember which ISP we were using 11 years ago ?
they even said that the city that I provided is wrong (although I'm 95% sure it's the right one)
This is more of a venting post, but if anyone here had a similar situation, any help would be appreciated, don't really know that to do.

EDIT: managed to verify the ownership! Thanks all for the replies.