Is it permissible to perform Umrah every year despite the father's objection to it, on the pretext of saving money, knowing that it is in Ramadan and its reward is immense?

If you have performed the 'Umrah of Islam' (the obligatory 'Umrah), then do not travel to perform a supererogatory 'Umrah except with your father's permission. You should try to convince him of the virtues of 'Umrah. If he grants permission, then praise be to Allah. Otherwise, do not incur his displeasure. Strive in performing regular acts of worship until he grants permission, because parents have the right to prevent their child from performing supererogatory Hajj, and voluntary acts of worship should only be sought with the permission of parents.