Car purchased from vauxhall with wrong tax disk

[Leefuller]

I purchase a vauxhall astra from the Go Vauxhall garage in Wimbledon on the 16th October 2013. The car was sold to me with tax on the windscreen until 31/01/14. It's now been 5 weeks. And today I have had a letter from the DVLA saying my tax has expired and was due on the 31/10/13. Obviously I've checked the tax disk on the car and at a closer look it seems the tax disk I've been sold with the car isn't even for the vehicle. After looking through documents and also the glove box I have found the actual tax disk for the car hidden in an old tax disk holder, I contacted the Wimbledon vauxhall branch and was simply told because I was sold the vehicle under the impression of 3 months tax it works out they only owe me about £40 so was told next time I'm in he area to drop In and they will put £40 worth of petrol in my car. And to either take it or leave it. No explanation as to how I had been sold a completely wrong tax disk , I feel like I've been conned and mis-sold the car but they said if they had realised the tax was due only 2 weeks after the purchase date then I would have Been charged for 6 months tax on top of he amount I paid anyway? Is this legal for them to sell the car under this impression? And am I being fobbed off with the £40 worth of petrol?:tinysmile_aha_t: