Pay as you go receipt?

I have the 3$/mo pay-as-you-go plan which I use when visiting the US.  For internet access, I buy a weekly data pass through the 611 customer service number.  Since the internet access is mainly for work, the firm would normally reimburse this cost, but the trolls in accounting need a receipt showing what was purchased and the amount paid.  There seems to be no way to generate an invoice or a charges/payments history for the pay-as-you-go plan through the website.  Am I missing something, or can a receipt be obtained some other way?  TIA.