CANCELLATION REF NUMBER ***7

After receiving a cell phone from MTN courtesy of a call from mobile plus I called mobile plus back within 2 days and told them I wanted to return the phone and cancel the whole arrangement due to what I was told regarding additional fees not mentioned previously.I was told to return the phone and all its contents ro the nearest MtN store. I returned the cell phone within 5 days of receiving it having not even made one phone call nor having browsed a single website.The phone was returned to Carlton Centre MTN together with the 2 sim cards and captured on the system.I then called Mobile Plus and told the consultant who answered the phone that I'd returned the phone and wanted to ensure that the cancellation was being processed...I then got a Cancellation Reference number ***7 from the consultant Leigh.I have also spoken to Laura and Chantell (and those are just the one I remember the names off).To my surprise today I received my second call from a law firm claiming I owe MtN R 1600...I owe MTN NOTHING! I have a freakin reference number for my request to cancel which was done well within the window period!What R1600