If they are plastic heels which are nearly hollow you need to fill them with a product called Stormsure. This is a glue which sets as a solid block. It is amazingly abrasion resistant, hard rubbery compound. I did the heals of my Timberland deck shoes, where the heels had worn at a horrible angle. The resulted repair lasted until the rest of the shoe were worn out. In fact the original rubber sole wore out faster than the repaired area.
Robert, November 2008