DPF filter issues over and over again

Hiya, I bought a van on the 29th January.
i didn't drive it for around 2/3 weeks as i had an operation.

when i did start driving it, the next day the DPF orange light came on so I took it for a long drive.
It happened 2 more times so i took it to the garage and it had a new filter put in (under warranty)
the next day i drove the motorway to gatwick and home again (about 3 hours) then went to mcdonalds and the DPf light came on again so i took it back to the garage
by the time i got there when they turned it on the light was gone but they had to change some outside temp sensor?

anyway since having it back Ive driven to gatwick and back again and today it came on AGAIN. I came home to ring the guy i bought it from and the mechanic who said to bring it back in and the light came back on when i went back to the car but when the mechanics turned it on the light was gone again and they could find no fault. They said basically something is obviously wrong but they dunno what

Can i give this vehicle back now? I paid £11000 and i feel like I've had nothing but issues, in total ie driven about 600 miles i feel like this is a lot of stress for such a small amount of driving. the guy that sold it says it just needs scanning but they scanned it the first time (when they put the sensor in) and said no issue came up, I cant keep driving a vehicle and having this bloody light keep coming on.

I just really wanna know if I have to keep this van now because I hate it, it was suppose to be a stepping stone for my business and its just causing non stop stress.