Complain

Hi I'm Clara Greef I've bought myself a fridge at Lewis stores in Parow(SHOPRITE PARK)in November 2021 on credit don't remember the exact date I start to pay my account in December 2021 First they told me the fridge was R10 000 on credit I manage to pay it finish,my instalment was R625 but I paid R700 every month,when I went to pay my last payment of the 10 000 they told me I'm not done the fridge is R18000 I told them that's not what they told me when I open the account but it's ok I then pay the rest of the money and Even a R700 extra...i never received a invoice or any letter from them,I then stoped to pay in May 2024 as I worked out my receipts and calculate that I've already paid my R18000 Nd even a R700 more In November 2024 they send the collectors for the first time I explain to them my case they even calculated my receipts with me and see Im done with my account but still demand me to pay a extra R7000 which I don't have In January 2025 they again send the collector, I'm a 72 year old pensioner I don't work only receive my grant from government What should I do in this case? If you can help me in this case I will appreciate it Thank you