I didn't take the time to fully read all of this thread, but going by the title, I had the same problem with Sign Warehouse. Not just their magnets, but other "house" products from them as well. Plus their customer service was one of the worst that I've ever experienced.
You can read more about my past thread and their magnets here:
http://www.signs101.com/forums/showthread.php?t=21261
After posting a while back on here about Sign Warehouse "house" brand of reflective material being junk "doesn't reflect, impossible to weed, etc.." someone from Sign Warehouse Pm'ed me on here saying that he'd fix the problems. So I messaged or called him (don't remember which) but I did try to get in communication with him, and never heard back from him. Initially before I even posted about the problems of the reflective, I tried calling my sales rep, he passed the phone off to his manager, the manager said that the reflective vinyl was over 30 days old, and that they couldn't take back the material because it was too "old". Pretty much what that translates to, is take the roll of material and stick it where the sun doesn't shine.
I still have the junk roll of reflective sitting in the corner, still in the original Sign Warehouse cardboard box. Every time I look at it, it just reminds me how awful of a business they run.
I'm not one to purposely bash a business, I understand every business can make mistakes, but I had done everything possible from a customers point of view to "work" with them. It is just that they weren't willing to "work" with me. Even after sending thousands of dollars of business their way, they treated me like a floor mat.
Someone on here recommended that I take my business to Fellers, which I have since done. Their service is top notch, they don't call to hound you every few weeks to buy stuff, they deliver to me in just 1 day, and overall it is a much better buying experience at Fellers.