Migration penalty

On the 23 Nov I did a migration from a mifi 5GB day & 15GB nigt contract R249 to a 10GB day & 10GB night for R299. Lucas assisted me and said I need to pay R100 for the change and I will not receive a new device and there is no penalty, he said there is not a new contract as he changed it on the system. On the 01 Dec I received a invoice for R1200 penalty fee. I went to wonderpark store and Lucas said he will phone back as he canot find the paperwork for the transaction, and he did not phone back. I phoned a few times without any success. He was never available again for 4 weeks, always an excuse from ***orkers. I phoned the store manager Mbulelo, he did not come back in two weeks, when I threatened him with the area manager he said I need to watsapp him and he wil sort it out, it is more than 2 weeks now and he keeps saying he is looking into this. I have not received any feedback from Mbulelo or Lucas and I contacted them on numerous times within the past 4 weeks. They dont even answer the phone in store, keeps ringing the whole day ***/1217 I told Mbulelo Im not willing to pay the penalty as it was not explained and he needs to reverse the transaction, did not come back