Four years ago we bought a house & paid painters to do all the woodwork in the house. The job was done in a week, looked lovely, the carpets were laid & we moved in. The paint started to chip off in places & we discovered they didn't sand any of the previous gloss & the new layer of paint started to peel/ fall off in places but we just painted over the patches. Four years later & I have big chips of missing paint where the top layer has fallen off. The new gloss isn't sticking to the old gloss so any minor bump & a chunk falls off.
What is the best way to resolve this? Do I need to sand down to the original gloss & start again or is there something better I can do?