How to find out the organization of SMS distribution by phone number?

Question

SMS

The question is as follows. Spam SMS from an organization located in my city constantly comes to my phone number and the numbers of my friends. The messages themselves do not come with the sender's name and not from a short number, but from ordinary +7 numbers. Numbers are always different, but all beeline. How can I find out through which mailing service they send SMS?! From a legal or technical point of view. Where to send any requests or claims. It’s just that on the Internet they offer to file a complaint with the FAS and Roskomnadzor ... but this is all a long time and no one will collect evidence there + there will be a mobile operator as a plaintiff. The very same firm whose services are advertised, just say it's not us - it's the intrigues of competitors.
PS It doesn’t bomb me, it’s just that there is an opportunity to roll out a round sum of money to them even in pre-trial order, because in court a fine from legal entities with 5 zeros + lawyer services + morality, etc. Therefore, I think they will agree to resolve the issue "peacefully", and the proceeds will go to charity. There are lawyers I know who are ready to help me for free, but I need some kind of action plan