As far as what he did, I have no idea. What i would do.... replace the belt and see if it happens again, make sure the tension feels about right. Im assuming since your asking for a mobile mechanic that your not too mechanic savy.... look it up online, replacing a belt is not a very hard job to do yourself, im sure there is articles online to walk you through it. If that doesnt work, ask a neighbor, im sure one of them know how, and last resort, look on craigslist for a mobile mechanic, there are plenty of them on there. Good luck.