Poor accounts reconciliation

I opened a pep credit account, upon the insistence of their sales reps in store. Initially I told them I really wasn't interested and they insisted on taking my phone number just so that they can keep in touch in case I changed my mind. As it were, one day I was buying stuff using my loyalty card and the rep there convinced me that it was more beneficial to sign up for the credit card as I could get more deals with the card and I signed up. All cool and great, then I so happened to have lost my cell phone and they said I could buy one with the card I had been approved for and proceed to buy one and made all my installments from the get go, and even paid extra just to try and clear the payments quicker. Then they sent me smses thereafter with banking details and a reference number to do online payments. I registered the bank details and sure enough their business was registered to do EFT payments and for 3 consecutive months I made the payments. On one occasion I was in store and paid directly at their teller and put in a little extra as before. Thereafter I started getting calls that my account was in arrears. I drove to 4 of their shops to show them the payments and all the shops were unable and the one was even unwilling to help me as they did not handle these things and gave me a number to call. I told them I did not have airtime to call and asked them to call their accounts department for me. I was given th phone to speak to them and got sent from one person to another and they were failing to help. Emails came through asking for POPs which I sent and was told could not access the pdfs even though they were given passwords. I sent screenshots of the payment confirmations from my smses as well as the pdfs and this time they said they were not allowed to use pics and needed pdfs!! I sent again and still no resolution. Then I started being bombarded with calls one after the other and several emails and eventually I went to my bank to get the POPs and managed to download then each and sent to their accounts and customer services departments and the several reps that emailed me. No acknowledgement of receipt of the POPs was made and yet I continued to be bombarded with calls. Several times I also phoned and asked them to check the emails with the POP and excuses were made about being in different departments and not being able to access those emails.... so I said the people emailing me and that I responded to should then check their mail and resolve the issue and up to now, 4 months later, I am being hounded at work and on my phone but have done everything I can think of to meet them halfway and now have extremely rude agents calling and refusing to listen and demanding while I am talking to them that I must call out the reference number of my transactions to them. Like one would memorize that in case of being asked. I have not missed a single month's installment and can't get this issue resolved and being threatened with blacklisting and marked as a bad payer etc.