LiceGuard RobiComb Sent half the rebate amount and made excuses Needham Massachusetts

Lice is going around at my child's school so I bought the robicomb to just make sure my child stays lice free.  I paid full price at the biggest box store and it had a rebate for $3.  Not much but for the price of a stamp I sent it in. Got a check back for $1.50.  There was a memo at the bottom that says "RobiComb Rebate("name of store"-adjusted due to combi" and that is where it cut off. I sent an email and asked for an explanation.  This is the reply I received:

Thanks for reaching out.

 The check is  less than the expected amount is because the rebate form that you sent in states that this offer “cannot be combined with any other offer, coupon, discount, or promotion”.  After reviewing the receipt you sent, it appears that your RobiComb was purchased at a promotionally discounted price.  This would normally cause the rebate request to be voided completely. We have decided to proceed in honoring your rebate request, by reducing the rebate amount thus completing the total discount to match the rebate amount.  

We hope this is helpful to you and again thank you for your interest in the LiceGuard family of products.

I paid the full price listed at walmart.  If it was a promotionally discounted price then that was between the store and LiceGuard.  I had no way of knowing it nor should I be punished for it. And then to act like they were doing me a favor was just adding insult to injury.