How to stop SMS spam from mobile operator? I keep getting SMS spam from Three mobile and I'm looking for a way to block it. The problem is that the SMSes don't come from a regular number, it just says "From Three" but there's no associated phone number.

According to Ofcom I should be able to reply "STOP" but there's no reply option for this type of special SMSes.

Is there any way to block this type of spam?

(I'm on Android 6.0.1, Xperia Z5)
I stopped this sort of spam from Three by forwarding every text I received from them to their own spam reporting number, 37726.

You will get an automated reply asking for the number that sent you the text.  As you don't get a number from the spam, just use Three's own marketing number, 0800 033 8002.

It didn't work immediately but they did take the hint after a couple of weeks.