Vodacom repairs fourways

Vodacom repairs four ways mall has taken advantage of me. I had booked in my phone for repairs and processed a claim with my insurance(vodacom). I fetched the phone from the store myself and already the phone was having problems which I thought was a network issue from vodacom network but later found out that the phone is actually faulty as a result of the repairs. All this happens in a period of less than 2 weeks. I returned the phone to vodacom repairs store at fourways mall to get it sorted as this is a fault from their side and now they are making all sorts of excuses just to charge me for the repairs to be done which resulted from their poor job. They are basically using the fact that my phone has a small crack on the back cover as an excuse to charge me. I am very unhappy with the service that I am getting as this is entirely a problem from their side.