As to what the shop done I dont know I was not there
But the best fix IMHO is get a new string and cable from gibblet.
The stock strings on Mathews bows are hit and miss as to whether or not you get a good one and by the sound of it you got a bad one that will just continue to creep no matter what you do.
The shop I teach in is a Mathews dealer and they got tired of having to re-tune bows because of string creep now every new Mathews gets a Bucknasty(gibblet) string and cable before they go out the door.