That isn't typically allowed. Spanish people also can have several given names, but they count as first names, not last names/surnames. A bank would typically check your data against a passport or ID and wouldn't allow you to put the middle name in the place of a last name.
And if for some reason you managed to do it, you would be called Mr. MiddleName in all communications.
As a curiosity, Spanish people often have the opposite problem - for example, in academia, if we sign papers in the "natural" way (FirstName FirstSurname SecondSurname) we'll be indexed as Name F. SecondSurname, which is quite jarring for us because we typically go by the first surname, not the second. So many (probably most) of us hyphenate (FirstName FirstSurname-SecondSurname) to avoid automated systems (or humans from other countries) to extract our surnames wrong.
What is actually a "middle name"? I have two "first names" meaning I can use either one I like, and in official situations I write them both in the first name field with a space (which works fine as such, airlines will combine them no issues whatsoever). What is the real life usage of a middle name in whatever culture has the notion of a middle name?
It is an other fun cultural context. I have Firstname Middlename Lastname. This or Lastname Firstname Middlename appear on somethings like credit card, ID, passport and official legal documents. But in normal live like receiving normal letters and so on it is just Firstname Lastname or Lastname Firstname. Even the order is fluid with Lastname Firstname being more formal.
And then some people have First-Name firstnames where either part is also a name, but whole thing is one Firstname... So calling someone with just First is often wrong...
Okay but is there any social situation where calling you by the middle name is the appropriate way? Except when you mom's angry like the other commenter suggested :) Is a patronymic a middle name, or a second (first, actually) last name?
And if for some reason you managed to do it, you would be called Mr. MiddleName in all communications.
As a curiosity, Spanish people often have the opposite problem - for example, in academia, if we sign papers in the "natural" way (FirstName FirstSurname SecondSurname) we'll be indexed as Name F. SecondSurname, which is quite jarring for us because we typically go by the first surname, not the second. So many (probably most) of us hyphenate (FirstName FirstSurname-SecondSurname) to avoid automated systems (or humans from other countries) to extract our surnames wrong.