Disappointed :(

I ordered a dell laptop for my classroom.  I called the customer service to make sure that I ordered it correctly because I had a tax exempt certificate.  So the rep told me to order the laptop and then send in the tax info to a number that he gave me.  I sent all the info to them and they sent back a form that they also needed filled out.   I did that and then found out that I because I ordered it with a personal credit card, they will not grant me the tax exemption.  I am so upset and now the school will only reimburse me the computer and shipping price because it is their policy that they will not reimburse tax.    It is disappointing to think that I followed the correct procedures and then to find that I was told the wrong information from a dell rep and that I will have to pay out of pocket for something that I shouldn't have too!  What a huge disappointment!

Any ideas on how I can resolve this?