product under guarentee not getting fixed

Bought R30000 Dell computer from Incredible Connection Clearwater which came with 3 year guarentee. Year later developed problem and returned to above shop who replaced motherboard. Only at home realized computer not properly fixed. Took it to Incredible Connection Menlyn Branch (Jonathan) on 4th April. He took computer in, could not fix and told me that Dell would call to assist him on Wednesday 8th April. I Followed up today just to learn that they have never been and I need computer back urgently.