Angry customer

Last year (2022) I took a phone contract in store and it's up to date. Then seeing that telkom is good, I took the 80G +80G Sim contract in July this year. The monthly installment is R199.00. The first debit order was supposed to go on the 20th of August but there was no debit order. Last month again there was no debit order. I didn't even receive a copy of my contract and monthly invoices. Now I got concerned and contacted Telkom to let them know that it's two months now without debiting and I am not receiving any invoice. I even went to their Facebook page so that they can assist me. The agent on Facebook said I owe R496.00 then I asked for banking details since they're not debiting. On Monday I made a payment of R300 then boom yesterday for the first time I received an email telling me that I'm owing R900 and they have been trying to contact me. As I remember I'm the one who was contracting them asking for a reference no and my account no. Today I made a payment of R200 then call to check if they received my payment and enquiring about the email. Hmmm, I was told that I must pay R900 because they handed over my account and I must provide proof that I didn't receive any contract. So the consultant told me that they have just updated my emai address,meaning that they didn't have my address all along. We agreed about the 20th since I get paid on the day but the consultant told me that it's written that the debit order goes on the last day of every month. Why are they charging me whereas they're the ones at fault. I'm the one who reached out cos I'm the customer and been paying my phone so well