MTN not sticking to the agreement

I took a data contract with MTN in May 40GB which was supposed to be 20GB a day and 20GB at night but since may until it was corrected in September i was receiving only 10GB for night. I contacted the lady that assisted with the contract and she rectified it and I didn't mind since i was hardly using the night data that much and the billing changed for October and i emailed called MTN who were giving me a long explanation about the amount was supposed to be R319 - the discount of R79.99 but i informed the agents and sent them my contract agreed that it was R239.00. R199 for the data and R40 for the router. I emailed MTN and got another reply from Nonkululeko who advised i was being charged for Caller line identify I emailed back to find out what was that and how to avoid it but never received feedback. I signed for a R239 contract and emailed this to MTN but they changing my billing to R240.01 and no one called or emailed as to why the agreement changed. Reference for the emails ***. Why is the amount different now and why was i not informed i'm not sure but MTN is not sticking to the agreement. I just received another statement now with the billing amount R240.01 and would like to know why as i signed for R239.99