Frontier most likely finally realized you were no longer a subscriber and closed your account.  Like someone else suggested, you may be able to recover your contacts from your phone or possibly a third party program if you were using one (Outlook, Thunderbird, etc).  

While it is frustrating, open an gMail account and move on.  You'll be happier in the long run.  I've had to deal with Frontier several times.  Once was a business service and my in-laws had residential service.  They had the worst internet service and even worse customer service.