Bad Service regarding default item

Good day, i am a very angry and upset customer from your Boksburg branch. Today 25/07/2020 i went to purchase a tv on special - the Sansui tv for R2999.00, the box was brought to the front - yet seemed like it was opened before was told they are all like that as they check the stock - they then plug it in so that we could see that the screen was working and no scratches or cracks - all was fine. Got home about an hour later and started setting up the tv - yes we had cut the two pin plug off(as we had nothing to plug it into) and put a three pin plug on. Plugged it in and switched it on, the picture is perfect yet the sound was distorted we tried everything thinking it was a setting yet it got worse and worse. decided to head back to the store to exchange. got to the store went to the customer care department - where we explained all of the above. young lady by the name of Danielle was helpful and said not a problem we will do a swop for you. Then the other lady(did not get her name) said we cant as it is a warranty void due to the plug issue. they then called the Manager - who didnt even great us let alone ask us what was the story just said sorry we cant help,you have voided the warranty by putting a different plug on and this is in the T&C's - she had then left without a word. The issue i have is this has happened to us before and the exchange was done no problem - no warranty or T&C's were explained to us and we were treated with the utmost disrespect as a consumer - we basically had to leave with a tv that does not work - R2999 is alot of money to anyone, and as a consumer to be treated like that is disgusting. Not even the Sales man who assisted us would listen and assist - he just walked away. i tried to look for the manager again and she had practically disappeared.I would like a solution to the above. please feel free to contact me on ***