ABS sensor broken by goodhope tyres - failure to replace

On Wednesday morning the 20th of Aug me and my husband went to goodhope tyres in Kuilsriver. We wanted to have both our 2 front tyres changed. This was done and we were given winrun tyres. Before we went to the place we called and asked if they had the same promotion that was listed in store for R699.00 per tyre the lady agreed. As we were about to pay Imran processed the tyres for R775 each! No indication of the promotion whatsoever. We were in a hurry and didn't think much of it. As we were driving the close to netcare in Kuilsriver we noted something weird happened to the car. The speedometer kept failing and the ABS light came on. We were headed to the hospital to sort out personal matters. By the time we went home this happened again. We wanted to stop by the tyre shop again but they were closed. My husband called the shop on Wednesday morning and even went there in person again. The problem still persists. The guys kept making up excuses about the back tyres needing to be changed too . It was because of an "imbalance". Utter nonsense! When we had our car checked out we were told that they damaged our ABS sensor ! And this will cost no little then 5-6k to fix. Who is at fault here ? Who must fix my car now? We cannt drive the car over 80 then we have this problem. It is extremely dangerous! I expect an action plan on when and how goodhope tyres will have this tended to. I would prefer to not deal with Imran again. You're prompt and urgent assistance is necessary for this query. Failure to do so will result in legal action!