RebatesHQ Deliberately Delays Rebate Payment

I purchased Print Perfect Platinum which had a rebate of $20.00 back on 12-3-07. The rebate was received on 12-13-07. Here it is 2-28-07. still no rebate. The rebate clearly states checks will be mailed 6-8 weeks after receipt. 11 weeks later NOTHING......I keep calling rebateshq and they all giving me different stories, Your check will be processed march 2 2008. Now they say you will receive your check by march 6 2008. What do I have to do to receive my rebate???