Cell C bad for business

I have a contract with Cell C and they suspended my line due to non payment. Now I have paid the account in full and they don`t want to open my line. This is very unprofessional from such a giant in the telecommunications industry. Furthermore with their incompetence I am loosing money because I am unable to work as my cellular phone is down. I was told that somebody would phone me immediately after I was in contact with customer service but up until now no response.