Unsatisfactory customer service from Wesbank is damaging my image

I paid up my BMW 320 series in 2017 and I haven’t receive the car certificate. I sold the car this year in January and I requested the car certificate from Wesbank. Wesbank told me many stories and promised to provide with the car certificate and I’m still waiting. The buyer of the car is on my case because the buyer bought the car cash and the buyer is struggling to register the car under her name. The sad part is that I’ve already used the money and I don’t know what to do.