I received a email from this Hahn collections with a settlement discount for my Sabc licence

I received a email from this Hahn collections with a settlement discount for my Sabc licence.I agreed to pay the amount offered and was told that my account will be up to date. Well I paid the amount and now they demanding I pay the balance that they promised to write off!!!! I have been sending them emails but they never reply. I called them and they now say that there was a error in offering me the settlement discount. So disgusting to take advantage of people. You can't even get through to Sabc to speak to them so where too from here ?