Can the third benefit of the Mobile feat prevent multiple creatures you attack in a single turn from making opportunity attacks against you that turn?


I am playing a monk. I wanted to use the Mobile feat, specifically the third option that prevents opportunity attacks, to do the following:

  1. hit creature 1 with my attack, then move away from creature 1
  2. then use Flurry of Blows on creature 2, then move away
  3. then make an unarmed strike on creature 3

…all without provoking opportunity attacks from any of them, thanks to the Mobile feat.

However, I was told that I can not do that because it only works for one creature and only my action is a "melee attack" or some such reason.

Is my interpretation right according to "rules as written", or am I misunderstanding how it works? It seems quite vague.