To be fair, would you really want your bank telling you “We’re closing your account because you’ve been a dick to our customer support agents”? Again, it’s one of those ‘can’t win’ situations, I guess.
My recollection, to put it this in the form that it was explained by a then-Monzo staff member, was they only block withheld numbers when they’re getting abusive calls. They don’t block specific customer numbers.
Found the quote. Admittedly, it’s not quite as I remembered it: