Etoll bill for a car I traded in.

I traded in my car the 16 of July 2015 and the same day we took ownership of my new car with my retained number plate and merc registered my same number plates BTW. I just received a sms from Etoll to that I am in a debt collection process for a car I traded in and merc failed to change the plates and drove to gauteng with my number plates under my name that's not only ***** now I sit with a Etoll bill and now my credit is affective. Absolutely appauling service from mercedez culemborg . Mrs Jamo ********** .