No tax invoice and totally ignored

I purchased an online course via Groupon on the 16th of April 2015. Since my company paid for the transaction, I required a tax invoice as proof and for auditing purposes. I have sent no less than four emails to Groupon's customer support department and, other than the automated response I received after the first communication, I have not received a single response from them. I am really very frustrated at being blatantly ignored and at Groupon's failure to provide me with the necessary documentation. This should be no issue for a company their size. I am hoping that this will prompt them to respond and send me my invoice!