Unreasonable amount deducted from refund

On 28 June 2025, my son accidentally bought R1400 of prepaid electricity for the wrong meter number using my internet banking. The wrong meter number belongs to Impact (UniPin), whereas our current/correct meter number belongs to the company Recharger. I contacted my bank, hoping they could correct the matter from their side, but after a week of waiting, they informed me that they couldn't. On 7 July 2025, I contacted Impact Metering for a refund. They informed me that they are only going to refund R850 as they are going to deduct R550 for a "call-out" fee. I never consented to the R550 call-out fee. In spite of that, they proceeded to cancel the token and only paid R850 into my bank account. Basically, Impact "stole" R550's worth of my prepaid units without my consent. As I used to live in the complex where the old meter is, I know that Impact visits the complex often, therefore I find it unreasonable for them to deduct a "call-out" fee in this circumstance. Their call-out fee of R550 is half a month's electricity for my son and myself. I find the R550 fee unreasonable and will be willing to pay a fee of R100 if a fee is unavoidable. I explained my financial situation to them: I'm a sole parent (my son's father passed away in 2006). I'm unemployed because of ill health and have been for many years. I'm battling to make ends meet. The R1400 was for two months' electricity to try and avoid the price hike on 1 July 2025.