DO NOT ADMIT ANYTHING TO THE DEBT COLLECTION COMPANY.
DO NOT GIVE THEM ANY INFORMATION.
DO NOT SPEAK WITH THEM.
You HAVE TO Tell them you HAVE NOT RECEIVED ANY LETTER,
The reason for this is that, if you admit to receiving the letter, then the clock has started for your 30 day response to the DEBT. If they don't hear from you within 30 days, then the debt is considered valid by the Fair Credit Reporting Act or something like that. This means you will likely have to repay the debt or hire an attorney.

You can ask them to send another letter of confirmation by mail, and to Please also put in any quesions they might have for you so you can reply by mail.
GOOD LUCK
Jim