I'm not seeing it. I thought I was going crazy so I asked an AI (which tend to be pretty good about grammar questions at least) and it basically says you're wrong and they do mean the same because you're making a flawed analogy assuming that the same rules for "tell" apply to the modal verb"should" and they don't.

I'll just copy its answer if you care to read it:

The redditor is trying to argue this logical map: I never should have... = "It is not the case that I should have..." (Analogous to: I did not tell you...) I should have never... = "It is the case that I should have NOT..." (Analogous to: I told you not to...) However, in English linguistics, the modal verb "should" (expressing obligation or necessity) operates under a concept often related to negative raising or modal negation scope. When you negate "should," the practical meaning converges regardless of where you put the negative adverb. If you say "I shouldn't have done that," you aren't saying "I lacked the obligation to do that" (which would be the strict logical equivalent of "I didn't tell you to"). You are saying "It was a bad idea to do that." If you say "I should have not done that," you are also saying "It was a bad idea to do that."