Handed to debt collectors for a service I never received

I requested Telkom to install a 10mb ADSL line in November 2017. I paid a deposit of R700. On arrival, the installer told me that 10mb ADSL was not available in my area. As I needed a fast speed line and Telkom could not provide the service, I asked for an immediate cancellation. The service was never installed and I never signed a contract. I never had the service in question for even one day. I sent various emails, spent hours on the phone to their call center (often on hold) and even took to their Facebook page to request assistance. Nobody could help me. I continued to get billed monthly.

I have now been called by a company called NuDebt requesting that I pay Telkom for the service I did not receive. If I do not pay, my perfect credit rating will be tarnished.

If feel completely trapped. Telkom is effectively *****ing money from me yet I have no choice but to pay it? I will gladly pay the moneys outstanding if they can provide proof that I signed a contract and that they in fact delivered the service???

I really don't know what to do. I feel ******