Vac/blower Bag

I have a Sears blower/vac; model number is 358-799370.  I admit this is an old model - it works fine, but the zipper on the bag doesn't.  This is my second bag and now it and the previous bag aren't usable because the zipper has broken.  Without the zipper, the bag is useless.  It seems to me that I shouldn't have to spend $27-30 to buy a new bag when the zipper is obviously defective.  I tried your customer service number and besides not being able to fully understand what your rep was saying, all he told me to do was to go to my nearest store. Any suggestions? Harvey Reinkemeyer