DVLA fine, Failure to Insure

[dotpc]

DVLA are chasing me for not having insurance on a vehicle I traded with a dealership at the end of March 19. They say I did not notify them of change of ownership at the time of the vehicles transfer to the dealer, I did, within a couple of days and sent the tear off slip first class post. In mid June we left the UK for a tour of Europe returning mid Oct19 to find letters, basically fining me for not notifying them. I was quite shocked, so called them to be told I should have called them after four weeks if I did not recieve notification of the transfer. I wrote to them explaining that I wasnt aware that they didnt receive the document that I sent them and I included the bill of sale from the dealership. They replied with a standard letter telling me that the fine stood at £100 but would be reduced to £50 if paid by the 11th Nov 19. I am not happy as i did what was asked of me, and wasnt aware that it was my responsibilty to chase them (surly that cant be correct). I still havnt recieved my vehicle Tax refund either which equates to 8 months. What can I do, I dont like the fact that this department seems to have total control over this and can hide behind words on a little piece of paper that i didnt even know existed.