dvla fine for a car i dont own?

You cannot get out of it. The DVLA send out a confirmation letter when they do a change of keeper which you are responsible for looking out for and questioning them if you have not had it within 4 weeks - clearly you failed to do this. It is detailed on the V5C that you send off.

You will have to pay the fine and also confirm in writing that you no longer have the car.

unfortunately, the onus of providing proof of sale is on you. however, there is an appeals procedure which is long and convoluted, and not really worth the bother. you can, however, try writing a letter giving the details of the person you sold it to, requesting the dvla contact the new owner at the address you provided. they have no legal responsibility to do this, but they have been known to do so on occasion. it may work, but ultimately, as stated by myself and others, the onus these days is on the seller.

You won't. Why didn't you pursue it when you had no reply from DVLA? Until they acknowledge that you aren't responsible you are liable, I'm afraid.

this is yet another step on the road to absolute state power you are guilty until you prove yourself innocent, you have no chance defying the government or one of its agencies its one thing you can't get away with in this socialist big brother paradise