Wrong billing

I changed a unit from 1 car to another with no problems only after all is done I was told I owe 2000 where this never happened before. I paid it now I'm asking for my subscription to be opened now I'm told to pay R1000. This is wrong to a customer and it's misleading while if you take a new contract you don't pay anything. So tracker wants new business and don't care about their loyal old customers