judgement

my son borrowed my tractor which in north carolina its not a law to have insurance on tractors.he never got a ticket and neither did the man driving the car who claims my son pulled out in front of him,causing him to run off the road,the law and me looked at the car no damage.months later i get notice that his insurance company payed him $3000.00 for damages.now they tell me i owe them $3400.00.i went to see a lawer.talked to his wife instead who was the secretary.she looked at the papers said not to worry she would take care of it.one year later i recieve a summons to court. i went and they had done tryed me a months ago without me being there,said they had put a judgement on me and i owed $3500.00.i was angrey,i refuse to pay.today another year later they send me a letter telling me if i didn't pay within {10}days of the date of this letter they would forward the judgement to the nc department of motor vehicles and request that they suspend my driving license until the judgement is payed in full which is $3942.79 now.how can they do this to me? i was not the driver,i was tryed without being present i am confussed about how the law works it wasnt my sons fault, the driver of the car plainly told the officer when i looked up there was the tractor give me advice please.