Quaker State/Shell Oil Rebate Center Owe me money, won't return my calls/messages USA

 I purchased two 5 quart jugs of motor oil at 2 different dates during the summer. I retained the receipts and went online to submit them for the applicable rebates. I went to the specified website online and uploaded both copies of the qualifying receipts at the same time. The website did not specifically state each receipt had to be submitted separately. It allowed me to upload and submit both receipts while only filling out one form. A few weeks later I received only 1 rebate check in the mail. It was also addressed incorrectly, missing part of my first name, even though I typed everything in correctly on the website.

I made a call to the phone number provided on the confirmation page, to ask about the rest of the money and about the incorrect rebate check. I called again 11/16/15 and left a 2nd voicemail. Once again, no call returned to me. I placed another call on 11/17/15, PRIOR to office closing and was continuously hung up on before someone answered my call. I called 9 times during the 5 minutes before office closing time and no one answered my calls. I left a 3rd voicemail stating my concerns and requesting a call back. Now my rebate has expired and I am unable to cash it. I purchased the qualifying items intentionally to get the rebate money back as advertised.