Are library fines for overdue books considered usurious interest, and is using library services in this case similar to subscribing to an interest-based credit card, and what must be done regarding paid or pending fines, and is it permissible to continue using the library when one cannot afford to buy books?

It is permissible to borrow books, and they must be returned on time. Whoever delays their return without an excuse is sinful. It is permissible to obligate such a person to pay a sum of money as a fee for the benefit derived from the book during the extended period. If the fee is agreed upon initially, there is no harm. If it is not specified, then the borrower must pay a customary rental fee for each day. This is not usury, but rather a fee for using the book after the loan period.