Deferred charging of international roaming bills, is it legal?

MTS strikes back.

I myself have stopped using the services of the rogue big three, but my wife does not agree with anything. She went to Italy a week ago (!), And today MTS sent her a text message that you need to pay more than three thousand, otherwise she will be turned off.
A reasonable person in me says that this is pure fraud, so I want to ask the habrasoobshchestva what were the precedents of dealing with this practice.
Since I have already said goodbye to money, I want to deliver as much difficulty to the MTS as possible.
I am ready to sue, let the amount and not very large (not a million, as in the story with a megaphone ), just to create a precedent. Write applications to the FAS, or where it is accepted to write them, on the topic of unfair information.
As I understand it, the MTS will complain that they do not receive data on conversations, but this is a lie. For some reason, TELE2 abroad blocks the phone immediately, and these unscrupulous rogues wait a week.
Rays of hate, burn in hell.

I really expect practical advice from you, I want to make our country better. :)