FNB is not making sense

I have a business account with FNB less than a month ago I got a message that it was overdrawn. My mother who is my business partner put it funds last week and yesterday they bounced back. Today she went to the branch and they told her that the account has been closed because it was dormant. This honestly doesn’t make sense because we did use the account in February and last year in other months we would just put some money but not every month and now it’s closed. This makes absolutely no sense at all