I think there is a way of masking the originating number and replacing the identity with a name, such as Airtel (and number as well?) ensuring that on your side the communication is threaded together with Airtel.
I was thinking that would apply only IF I have a contact number for an entity named Airtel, no?
But if it's possible, then the SMS provider is committing an illegal act (impersonation?) and so should face legal action from the regulator.
I think it would be really sloppy of them to consistently contact you fraudulently as they risk their own exposure.
Even IF they constantly change the numbers, the next question would be - are those numbers registered? To whom?
If there was an entity interested in tackling these issues, all they would do is look at my incoming call logs (on the Airtel line) as well as the SMSes purporting to come from Airtel (if the masking is actually happening).