Diageo did not receive correct amount on rebate Winston-Salem North Carolina

 I purchased 3 bottles of a popular rum as rebate value increased with each purchase. 1 bottle was $5 rebate, 2 bottles was $12 rebate and 3 bottles was $20 rebate. I purchased 3 bottles on separate occasions within required time frame and submitted all 3 receipts with 1 rebate form. I received a rebate check for $5.00, not the $20 that I qualified for. When I call the # on the check, it is all automated with no option for customer service. I have extreme hesitaion in purchasing any further products from this company as I feel deceived.