Impossible to get a response!

In November we bought a second hand Kia Picanta. We were told we would be contacted with regards the papers and licensing of the vehicle. We thought there was a leak when we got home, and Charles told us it was the air conditioning, but would check it when we went for a road worthy which they would organise . . . which has not happened yet. We have tried on numerous occasions to make an arrangement but nothing has happened. After complaining by email Charles emailed me and made an appointment for me to take the car in to get a roadworthy, and I took time off from work to take the car through, Charles was not there and no one knew anything about it. I spoke to another salesman who promised faithfully to get back to me, but I have heard nothing. We put a complaint up on their website in March ... but have heard nothing. I love my little car, but find the after sales service is disgusting. I think we know the names of every single staff member at Kia, having spoken to just about all of them. We are not sure where to turn now - we have had 5 months of being messed around, and have tried contacting head office, but just get put through to Customer Service. Where do we go now.