[Koha] fines keeps increasing for check in items

Hello, pls i have this strange question that i need an answer to. A patron that borrowed book and Accruing fine keeps increasing despite the return of the book and when I check the account of the Patron most of this added value to the amount after the return of the item(s) is/are always with either FU and some with F under the account type. What can be responsible and what can be done. I am using Koha 3.22.04.000 on Debian 8.2Thanks