My personal registration number is locked by we buy car

I've sold my tiguan to we buy cars in Cape Town. I told them that I need my personal registration number. All to found out that they have locked my personal registration number we vw wanted to register my car. I was promised by the buyer that it was sorted out I could get it and it's still locked. Buyer is not picking up the phone. I need my car tomorrow with my personal registration number. This car was sold in September and it is not acceptable.