Registration forms missing

We came in the office this morning & found out that 86 registration forms are missing.  How could this happen?  How can we get these back. 

Sorry for the inconvenience this may have caused you. 

Your account was recently downgraded to a Free account and considering that the Free account can only store up to 500 submissions, some of them were removed from your account. Considering that you upgraded the account to a Bronze plan I was able to restore them. Your form now has 171 submissions.