how can i have my buffy pay for my car they ruined while changing my oil with them?

I took my 2012 subaru to have my oil change with buffy. after the oil change everything was fine until i smelled something when i got home a day later. I opened the hood and found out that oil cap wasn't locked and the oil had leaked into wrong places. when i asked them to fix it, they said it was insurance problem and insurance said it is their responsibility. the car is been fixed now out of pocket. i am debating how to get them to pay for the damages which is about five grand.