Airtel — 4g sim card activation issues

When i send my new airtel sim number to 121 it says not a valid keyword please send help to 121.

This makes no sense at all. Online its just asked to send this sms and then wait for the old sim to deactivate and the new sim will work in 4g which is not helpful.

Airtel network is going pathetic day by day. Here in rabale the 3g services as well do not work. I was told 2 months back that the issue will be resolved but is still the same.

Please help and advise!