Is it permissible to use a credit card with full payment without interest? And what should I do about a debt that has not been paid because the bill did not arrive after returning home? And is it permissible to give charity equal to the amount due to the accumulation of interest and the difficulty of direct payment?

It is permissible to use a Visa card if it is free from usury. However, if the contract stipulates that late payment incurs usurious interest, then it is not permissible to use. It is also not permissible to pay the interest resulting from late payment, as it is usury itself. As for the money you took but whose bill did not reach you, it remains your responsibility, and you must deliver it to its rightful owners by any suitable means. If you despair of delivering it to its owners, you may record it among your bequests and donate it on their behalf.