The villagers wont reset there trades

I am playing on a realm and i am trying to get a villager that will sell mending books so i got the villagers to a area close to my house and put a hed in it and got them to the job i needed and then after a wile i got paper to level them up and i didn't get the trade i wanted so i tried to reset there trades but they would not i tried to get rid of there bed and even punched them i also went back to were i got them from and tried to find anything that would keep them from changing to a regularly villager i cant find it but i assumed it was a bug after a while