MBD/Vodacom claim of money owing.

I've more recently started receiving SMSs from MBD Lawyers, saying there's a document waiting for me. It said I had to enter a pin to open the document. Each time I attempted this I would be told I had entered incorrectly, and as careful as I was, on the third attempt would be told I had used up my allotted number of attempts, I must call them! I am a pensioner and cannot afford expensive cell calls. I checked my emails, found nothing from them, then thought to check my Spam box and found what i thought are unprofessional emails from them, in that there was no addressing of myself, and no ending with the name of the person from MBD. The email stated I owed Vodacom R998 dating back about two years from when my contract ended, which I don't! I have roof of this! I have since on a number of times emailed letterheads to Vodacom instructing them to deduct my then monthly payments, from an amount I had paid forward for my two contracts. This they did successfully for six months, and sent me statements showing a zero balance. I sent copies of these statements also. There was other documents also sent to support my claim of my not owing Vodacom anything. My gripe should be with Vodacom also, as they like MBD, seen to be a bunch of *********** idiots, and don't seem to have any inter departmental communication regarding this matter. To get back to MBD, I have sent them and their collection agency more than three emails each with all the proof of my payments, including bank stated proof of payments, but they persist sending me SMS's and Spam emails, but have never responded to my emails sent to them!! My question is, do they ever read their emails???