Here is what I have done several times in similar situations (_not_ with Lingo, however). After discussing the matter with a phone rep, I will write a brief summary of the conversation, including all the details about what will (and, if relevant, what will not) work. I then e-mail it to them and ask that they print it off on their letterhead, have it signed by someone of manager level and fax it back to me. When I've got the fax in my hand, I give them my credit card number and an authorization to proceed with the order.
If they won't do that for you, you probably don't want to deal with them.
Cheers,
Henry