Is imposing a percentage fee on cash withdrawals made using an unsecured credit card—the loans of which are paid by the cardholder's father—considered usury, bearing in mind that there are fatwas that permit charging a percentage fee for cash withdrawals in return for services, and others that consider cash withdrawal a permissible loan as long as it does not lead to an usurious increase?

What you alluded to is that cash withdrawal using an uncovered card is considered borrowing from its issuer. If this results in the issuer taking interest on the loan, either through a late fee, or by deducting a known amount, or a percentage that does not correspond to the actual service of withdrawal, then this is considered usury (riba). However, if the percentage deducted equals the actual fees for providing the loan, then there is no harm in it. The criterion is: Is the deducted amount in return for actual services, in which case there is no harm, or is it in return for the loan, in which case it is usury (riba)? Most often, these fees associated with the loan amount and deducted upon withdrawal are of the second type, and are not actual service fees.