Cell contract upgrade under false pretense

Shocking service. A salesperson from SummerMobile called me to say that I'm due for a cellphone contract upgrade. They can offer me a better deal if I keep my phone device. I agreed. Needless to say I was billed 3x the amount I was told I would pay. According to them it was Pro-rata and early cancelation of my contract. This was not expkained to me. SummerMobile says it's Mtn who needs ro reverse the payment and Mtn says it's the 3rd party Summermobile. I'm stuck in between and had to pay. Expensive lesson learnt ... never buy anything via these ********.