R30,000 invoice linked to a number that is not mine

I received a bill for R30000 for a cellphone number that is not mine, but is linked to my account. I have spoken to numerous agents and contacted them via their social media pages as well. They have hidden my comments from their social pages and refuse to give me a time line as to when this will be sorted out. This query has been ongoing and it is now the weekend. Debits are due to run off next week and no one will provide any answers. This phone number is not mine. I don't understand how these kind of errors can occur. The agents are nonchalant and don't seem to care.