****py billing

I subscribe for an Mtn contract which I am supposed to be paying R349 every month. However, every month I am paying like R750. I am always told I made international calls, whereas I didn’t. I did not receive any international calls in fact. They always say I used an extra airtime which is a lie cause my limit is at 0. I am tired of this mtn ****py billing. I want to even cancel my contract ?. I am infuriated. This is so unfair