Repair - Consumer Complaint for PEP STORES

I purchased a Samsung A2 in November 2019, in June 2020 it started giving me problems it would say phone is overheating and I should switch off some apps then it turns off the problem persisted I then decided to take phone bad to the store I purchased to be sent for repairs under warranty on 30 Aug 2020. On 17Sep I got a call from Margo saying the assessment was done an they found liquid damage and I will have to pay R2600 for repairs I said I dispute liquid damage and that they must bring back phone. I asked also for proof of physical damage which they refuse to send and they say I must pay for assessment R171 which I was not made aware that I will pay for assessment. Please how can they charge me and refuse to send mr proof. Please assist me to get my phone back as it was as they refusing to bring back my phone.