I have had great success when I've contacted manufacturers directly when I've been unhappy with a product.
I, too, had problems with my ATG gun when I first purchased it. I bought it when the pink one came out in Michael's. I could not get the tape to lay down well - it got all gummed up. I looked at the tape roll and it wasn't wound tight. I called 3M, they sent me new tape and a new gun, as well as a return shipping label to return the wonky tape. You really can't ask for anything more than that!
I recently called the manufacturer about a bottle of useless Goosebumps I recently purchased. I couldn't get the spray bottle to spray. The customer service rep I spoke to apologized and promised to send me a new bottle. It took a while but the new product arrived yesterday and works great.
I most often get the contact information off the product itself.
big time supply collector
part time scrapbooker & stamper