2004 Chevy Aveo Timing Belt maintenance Schedule

Warranty problem
2004 Chevy Aveo 4 cyl Wheel Drive Type unknown Automatic 70000 miles

I'm having a huge expensive fight over my never-used warranty. I purchased the top of the line Gold warranty with Auto Warranty Services and while driving my Aveo, no previous problems, the timing belt broke, damaging valves, etc. I filed a claim with the warranty company and they are stating that when I had oil changes, the shops doing the oil changes should have recommended timing belt service at 60,000 miles and this wouldn't have happened.I am currently faxing them proof that I have had oil changes done, on a regular basis and no such recommendations are on the invoices. SO>>>>
just how much of a difference would this have made had I had it "checked" at 60,000-? Please respond. Thank you.