Unable to use cancelled tickets when booking new flights

[Daughtry22]

I have a number of unused tickets due to many last minute changes in recent months.  I've tried using them as credit when booking new flights.  It worked once, but the last two times I did it, I received an email saying that my 'special request' couldn't be completed, so the full invoice price was charged to my card.  There is no email link to ask for clarification, and the email itself says that the address from which it was sent isn't monitored.  I just want to know what I'm doing wrong.  Is there a number where I can talk to a human that can explain it?

[KevinD]

@Daughtry22 the best way to ensure unused tickets get used is to call your company's travel agency. Ultimately, they are responsible for applying unused tickets, so contacting them directly is the best option.

[BEngelke]

Were the tickets on American Airlines by any chance? We've had a similar issue because AA changed our cart number so a half dozen unused tickets can't be used. I've been told the cart number changed due to AA eliminating their small medium business rewards program and eliminating any corporate discount programs. Haven't been able to find out if we have any recourse yet...