Airtel — 4 g sims not delivered but got message that it was delivered

Address:

Dehradun, Uttarakhand, 248001

I received a message that the sim that i ordered online for my mobile for changing from 3 g to 4 g were not received till now although i received message from airtel that "dear customer, your 4g sim has been delivered at your premises. To activate the new sim sms sim ti 121 and enjoy 4g speed at 3g prices. For further assistance, sms get4g to 121.
I asked my postman and he said he did not get so how can he deliver.
I do not know where they delivered and what happened to sims.