Bad after sales

Purchased a computer in 2018, some parts under guarantee for 3 years. Just before lockdown had problem with CPU, took it in they sent it to supplier but could not be checked before lockdown. I then purchased another CPU as was told they would exchange when back from suppler. I paid R5000 for original and R3000 for the new one. I now get a R1500 voucher back which is not acceptable.