Sold an Audi with a sidewall repair on the tyre

I purchased a demo Audi from Audi Centre Hatfield in 2014, I have been the only owner of the vehicle since purchased, earlier on in the year when I had to get my tyres rotated I found that the front tyre had a previous repair done to it on the inside sidewall, a repair that is not considered roadworthy. This was obviously done while the car was still at Audi, I contacted them and they are taking no responsibility because it was only found 3 years after purchasing the car. I'm just lucky that the ***** repair didn't burst while I was driving. Audi don't even want to take responsibility and pay for the replacement of the tyre, they simply offered a fuel voucher.

Disgusting that you trust companies to be honest and have your safety in mind when purchasing something such as a vehicle, however they allow such ***** repairs like that.