Worst car purchase I've ever experienced

I bought a car from them five months ago, the car was purchased cash and till today the car's notice change of ownership hasn't been done, the roadworthy certificate which I paid for has even expired because of the delay. I've been getting the run around buy the sales person and their service agents, I can't renew the almost expired disc because the car is still registered under their company. Worst car purchase I've ever experienced