Worst tyre dealership in Gauteng

I bought secondhand tyres from this dealership "TYRES FOR AFRICA" in Midrand Gauteng, the guy working there inspected the tyres and guaranteed me they are in very good condition. I had them fitted two days later, as I am from Lephalale, on my rims and the worker pointed out that there are bubbles on both tyres. He did however managed to balance them but the steering wheel shakes like crazy above 80km/h. I immediately contacted the dealership and showed them the bubbles on the tyres and requested a refund. They refused, I tried to get them to give me other tyres in return but that they also refused saying I have to take the loss.