Best way is to buy cheap tubbed adhesive
Spread on the wall leave it 15/20 mins ,
Then scrap off,it will bring all the paint with it .
Slightly messy but if you scrape into a bucket or tub it's the best way.
Personally I don't think it's great ,definitely contact the tiler he might hold his hands up and come up with some solutions to fix the problems. Hope you get the result you want