Virgin accounts a mess

I cancelled my contract with Virgin Mobile almost 18 months ago, in November 2013. I followed all procedures, e.g. gave a month's notice (even though my two-year contract was at an end), checked my account was paid up, before porting my number to Telkom. My account was paid every month, in full, via direct debit order.<br> <br> Since then, at various intervals, I have been threatened and harassed by Virgin, Shapiro Shaik Defries and Associates, and Virgin's debt collectors MBDLC, saying I owe over R1000.00. I have made calls, written emails, provided copies of my contract and reference numbers for calls. I have received no responses, and no account statements detailing where they got the amount from (I was also charge R20 a month for itemised billing, which I never once received). Now I am being threatened with blacklisting.<br> <br> How could I wrack up such a bill when (a) I paid by debit order (b) settled my account and added pay as you go airtime in case the transfer between Virgin and Telkom took awhile (c) my Virgin SIM has not been in use since 17 December 2013? And why would Virgin port my number if my account wasn't in order? I am considering legal action.