Sick of overbilling and threats

Why can't Cell C sort out my bill? Since my contract expired, I have been receiving extreme statements and continuous threats. Every month I need to phone Accounts to sort out the total, just to be threatened the following month. Last month Portia assured me that R296 will cover me to the end of May, but the email I received today threatens that my service will be cut immediately if I don't pay R185! How is it even possibly if my monthly installment is only R96? I am sick and tired of this nonsense. Cell C, get your act together - I will definitely not miss you