Cell C **** people

I have a contract with Cell C for about 10 years. Never had any problems with calling other numbers. Last year I upgraded and added another contract. Now if I phone certain numbers (0860 or 087) I get a message "if you are on a pre payed please load"or something to that effect. Now they inform me that it is not an open line I need to recharge my phone with a prepayed package. Never had this before. since when must you recharge your account when still have air time on? this is a **** from Cell C and is a breach of contract. I am seriously considering canceling both my contracts. I will be stopping the debit order at the bank as well until this matter is resolved to my satisfaction.