Overcharged on my monthly installment

I have been with Matrix since 2018. In June 2024 Matrix called me and advised that they need to upgrade my tracker. They advised that my new instalment will be R195. End of june i was charged R299, July R440. I called in July and asked why I'm charged R440 when I was advised that my monthly installment will be R195. I was advised that I was charged for the old and new equipment as the old contract was not canceled. Adjustment will be done on my account and in August I will be the difference. Come August I'm charged R440 again when I called I couldn't be give a clear explanation. In September I paid R195 and received sms starting that i need to pay R465. I called Matrix to request if my account can be corrected because the error is on their side but nothing was done and still no explanationwas given. In October I paid and received an sms that I need to pay R156. This is really frustrating. I than decided to cancel my contract and they now want me to pay R3941 for a mess they created for me. I was never sent the copy of my contract which i was advised will be emailed. Matrix is so quick to tell you how much you owe them but can't assist in resolving queries.