Shein under declaring customs

Hi. I have a huge problem. My parcel has been held at customs office due to penalty fee. SHEIN sent them a false commercial invoice stating that my parcel costs less than R500 even though my parcel costed R1575. Now there is a pernalty fee of R750 which must be paid which I declined to pay because its not my fault that shein unde declared my parcel. I have been going on and off with an agent for a week now asking for a refund an I have not been assisted. I did not get both the parcel and my refund. Instead SHEIN offered to give me 100 points instead of my refund or paying the penalty fee.