phone blacklisted and I paid them

I was blacklisted by cell c for not paying so they handed over my account to their lawyers so last year December on the 23 I paid them off but the gave me wrong reference number so the asked me to e-mail that proof of payment I did that so now I call them so that they can open my phone their consultants keep moving me from one person to other and they tell me that the person who close my phone is nolonger working the anymore so I ask how is that my problem cause they still can ask someone else to open it they tell me stories that are making me angry I'm not happy on how they are handling this matter and know yesterday I was called by their lawyers telling I owe them but I paid them full amount that they told me I owe last year 23-12-15 till now