I recently had a session where it became apparent to me that I had to increase my 5th-level paladin's charisma somehow, having already used my Ability Score Increase (ASI) to increase my Constitution and Strength (my paladin is acting as the primary tank and wanted the ability to use the biggest armor in the PHB).
Our GM said that if I could give enough reason, story, and have my character use enough ingame time, I could choose a feat that could increase my charisma. This limited me to either Actor or Resilient.
Actor made no sense in the type of character I was playing (He views acting as lying, trying to appear as something you are not), so I wanted to take Resilient for the charisma ability.
Being a paladin, I already had proficiency in saving throws using charisma, and because of that, several of the players as well as the GM said that I couldn't take that feat because I already had proficiency, meaning that the only other feat that could increase his charisma was Actor, and that did not fit my character at-all.
I have tried reasoning with them, that it doesn't mention it anywhere that I can find, that I can't do that, and the only response I got was that "It makes no sense why you should be able to take a feat for something you already have proficiency with".
Question: If a character has proficiency in saving throws using the same ability that a feat grants proficiency in, does that prevent the character from gaining said feat?