Hi. I am so sorry you are having a hard time redeeming your vouchers.
I have redeemed vouchers by doing both the ticket by mail and going to the airport to ticket. In both cases, I let the agent know that I was redeeming a travel voucher at the beginning of the call.
I was not charged anything calling the call center to book flights, since you are not able to book using the voucher online. I am just a Premier member too. If I had called to book a flight sans vouchers, I would have had to pay the fee.
I am surprised they charged your credit card - I have done the tickets by mail and my card was only charged the balance (which was only something like $10.00). The only reason I did it for that booking is because my best friend gave me her vouchers since she is out of the country and was not able to use them. I had to mail in a copy of both my license and her license along with a letter indicating she was booking a flight for me. There was no agent booking fee for that transaction.
The other times I have just gone to ORD to handle, and I just did this as recently as last week booking tickets on behalf of someone else.
I hope that you are able to get everything resloved and you are reimbursed. Please let us know how this turns out.