Rejection of claim

The policy is on my name and I am responsible for paying the monthly, my son is the regular driver, the finance for this car is also on my name, with applying for the insurance all was declared and that my son has an arrangement with paying a school that money is owed, now in June somebody drove into the back of his car, now that a claim is forwarded to them, they reject it due to default against him, he has never claimed from insurance fore a accident ore theft of car which is relevant for insurance, I just dont know what to do and this car is still financed and with the damage on car we wont get insurance, they said with the policy is also cancelled, please help