Try again as the error may have been due to server caching an old database.
If still not activating..no worries it will be released on app soon and missed call activation will stat next Sunday.
Your base pack doesn't matter. New SSS offer will start working within 2 days and DBR 1 topups should work even now.
Just post the reply message from Airtel SMS (remove customer id and post).
If you have 2 RMN then try from other mobile.