Spam invite from player not on my steam friendslist#2890

I am getting spam invited by what I am assuming is a bot who is not on my friends list. I cannot block them with just the username and I have no way of knowing their steam ID. There is also no way for me to stop them from sending invites in game and the options to not recieve game invites through steam does not prevent it from happening

Explain what is happening exactly when you get spam invited?