sales tax exemption

This another sales tax problem that I hope Comcast_Phil can help with. I work at Methodist Children's Homes. We are located in Jackson, MS. We have a sales tax exemption letter from the state saying we are not required to pay sales tax. The letter specifically states we are covered under MS Code Ann. subsection 27-65-111(e). Specifically, we are covered under the section for orphanages, old mens or ladies homes, supported wholly or in part by a religious organization. We also have an IRS designation as a 501 c(3) charity. We have provided Comcast copies of our sales tax exemption letter numerous times, but we keep getting told that the sales tax department at Comcast has rejected our forms based upon where they have us in the Comcast system, which is "nonprofit/charitable religious". The customer service people refuse to give us a phone number for the sales tax department. 

Entergy, Atmos, the City of Jackson, Walmart, Home Depot, Office Depot and numerous other companies recognize our sales tax exemption,but Comcast refuses to even talk to us. How do I get this problem corrected?