Another Portfolio

for about 1 week now me husband or i have received numerous phone calls from a debt collector called Portfolio Recovery Associates. i searched it and it does seem to be legit. but from day one she began speaking about a letter that was sent out long before she ever started calling, we never received a letter. she claims she sent out another about 10 days ago and we still haven’t received it. we get all of our other mail why aren’t we getting this letter? also, she asked if she could fax it to me, i told her yes. i gave her my WORK fax number. and that was about an hour ago. i still haven’t received a fax. she is also VERY adimit about me setting up an automatic with draw from my checking monthly, im not comfortable doing that and as soon as i mentioned that she said well it will be another 5 dollar charge if you use a credit or debit card to pay the payment. she claims she is trying to make it easier but the further we go along with this the more difficult it gets. what should i do? can i call the past credit card company and ask whom the account is now with?