Should I consider this theft?

I am getting highly annoyed with Teljoy. I had a PS4 and Laptop with Teljoy (Account number ***) and I opted to settle these in full to take ownership in August 2019. I paid an amount of R 11 795.90 on 29 August 2019, and received a settlement letter on 30 August 2019, signed by Selina Dube, Collections Administrator. All was fine, or so I thought. Then at the beginning of this year, 2020, I needed a new washing machine, so I got one through Teljoy. Now the amount I am supposed to pay is R 289.00, however I have been charged R 608.93 for several months. I sent emails to query this and received no response until I threatened to not pay, whereupon I got a call and was advised that an error was made my Teljoy and that they had continued charging me for maintenance etc, for if the Laptop breaks. I said I never asked for that and was done with any and all dealings with Teljoy after paying the Laptop in full and I was assured that the additional monies, which come up to R 319.00 per month, would be credited to my account. Teljoy has not only failed to honor this, they have also continued to charge me R 608.93. I then contacted them on around 27 June 2020, to request a statement showing that the amounts have been credited to my account and i instead receive an invoice for an amount of R 289.00. No statement. I have sent emails to the following Teljoy staff: Shouneez Naidoo <***>,Ashton Joel <***>,Thando Mbambo <***>,Chantelle MacKenzie <***>,Vuyo Ndamse <***>, Teljoy <***> querying the matter and have NO RESPONSE WHATSOEVER from them. Is this how you do business? I expect a response to my queries or I will take this matter to the Consumer council. For such a large organisation, your customer service is absurd and your failure to respond when you have in fact been in the wrong, is appalling. I expect someone to get back to me because in my eyes, right now, you have ****** that money over a few months, so until it is either credited to my account of refunded to me, I will treat it as THEFT and I will take further steps if you fail to address this matter with me.