Yeah, ignore it , I had one in Jan and did not reply to the three letters, its not a con ie its not illegal what they do but very dubious, as mentioned it’s at best a breach of contract which is for them to prove. Very difficult to do as they have to prove the contract is with you and just because you are the registered keeper of the vehicle does not prove you were the driver. You are under no obligation to tell them! So they can’t prove it, they know this so don’t persue it through the courts. Ignore it, you will be fine.