Unfair treatment

I started using cell c contract phone last year and it was good all these months and it happened where they extended my installatment from R321 to R391 then I skipped a month not paying them which was August only but all these months were busy dedicating it fine so now they closed my phone and dedicated R500 and also R212 but my phone is still closed so this is so unfair when I call the customer service they telling me they don't know what's going on but I must wait 2days while I paid them and they not giving me the closing balance for the whole contract.