rebate

I came across a rebate offer from RainX - It was: buy 2 rainx products - get the 3rd free - two offers per household - so I bought 6 wiper blades for which I was supposed to get a $10 rebate from each for a total of $20. When I inquired as to why I never received the $20 they told me it was because the products had to be purchased at Menards and I made the purchase at Pep Boys. No where on the rebate form did it indicate that - they even acknowledged that - yet they will not honor the rebate. What government agency can I make a formal complaint with regarding this?