What strings did they put on? How many shots on them? Sounds like a poorly made string set. A 90* turn after months of shooting is a lot. Look and make sure you don't have any broken strands or serving unraveling. Also make sure the peep didn't move. That isn't very likely but will twist the peep. You will need a press/shop to get the string twisted and straighten the peep.
A good quality string will break in in about 20-50 shots. After that any peep rotation during the life of the string will be very small, if any.