Client power

Not so recently I was employed by Css solutions powered by ison/brooks and luyt attorneys working the Fnb core portfolio which is the business accounts debt collections department. So Css has a promise to pay rule which is you only benefit what you have arranged. That means if you have an arrangement of R5000, and the other party pays R10 000 you only benefit R5000 that you have arranged and the other R5000 goes to the company. So I made a mistake on one of the accounts I was working on. I gave a wrong reference number which paid into a different account. The arrangement was For R10 000 and the reference number I gave the arrangement there was for R3600. The person paid the R10000 but the money went to the R3600 account. So I was told I need to pay back the R10000. The R3600 account was owing for more than 5 years and it was a credit card account. Once the money got into the account the owner got a notification and saw the money and took it(R10 000) and he was due to pay R3600. In January I was told my the call center manager by the name of Prisca Khanyile that I need to sign an aod(acknowledgement of debt) for the R10 000. So my argument was why should I pay R10 000 when I only benefited R3600 according to their own promise to pay rules? Mind you I was still on a 3 months contract which was due to end on the 28th of February 2026. She advised me that if I sign the aod she'll make me permanent so that I can be able to pay the money back in installments. Because I wanted to secure the job I agreed and was sent to the payroll department whereby we arranged to pay R300 a month. On the 13th of February I was then advised by the same call center manager Prisca that FNB wanted me out of the portfolio and they need to get rid of me. They then gave me a termination letter stating that my last working day will be the 28th of February 2026 which I signed. On the 18th of February 2026 I sent an email in the morning to my line manager Farayi Sanika for clarification and to my surprise the very same day I got a second termination letter stating that with immediate effect I must leave. In the early termination letter it stated that I will receive my full salary and whatever is due to me but to my surprise I was never paid.i followed up with emails to Joanne maseko who is the payroll manager and was told that Fnb advised that they shouldn't pay me. That on its own affected my health and I had to take pills called Prednisone for the next 5days. Right now I'm unemployed because Fnb adviced my company to get rid of me.(Which might be false) I couldn't even pay my child's school fees and transport because I didn't get paid. Does a client have that much power to fire someone that doesn't work for them ?