Slashed my tire

I had the most awful experience at Bestdrive that i will never take any of my vehicles back. I brough in a trailer tire to be repaired. The guy took it to the bath and tested. i was with him and saw that there was a pin ***** of a hole on the tread and nothing else. I bought the tire this year so i have used it may be on 5 trips. It was in really good condition besides the leak. They repaired the leak and off i went. Upon arrival at my house i noticed that the tire was almost flat. i live 300m away. I took it back and gave it to them and asked to check the repair that they had done. I then took a phone call and walked away. I saw them looking and looking for the leak. I walked over to Spar and when i came back they showed me a cut on the wall. It looked like a knife had cut the wall as long as a 50-cent piece. I said i didn't bring it in looking like that. They refused to take responsibility and said that i must buy another tire. So basically, they slashed my tire so i can buy another one.