Before you start getting into the seller, who appears to have done the job requested, could there be other reasons that these things changed, server updates, web software updates, just a bad day for those functions…?
Now it it stays that these things have been changed, first thing would be to have a talk with the Seller to see if they may have answers as to what has happened. They may know and help, they may know and lie, they may have idea or no ideas. Give them a chance first.
After that, you can see if it seems likely they broke your site (and are unwilling to fix it) or if it was something else in which case, lucky you didn’t blame them.