Airtel — not issuing invoice for sim replacement

Hi,
Recently my mobile network failed on its own, nothing was disturbed.
I went to airtel store and they told me to replace the sim card by paying 25rs as fees.

My questions :
1. If the sim is not physically damaged, why should customer bear the charges
2. They take 25rs while sim mrp is 5rs.
3. They won't issue gst invoice for the same

Airtel has converted this as source by deactivating the sim from backend and promoting customer to pay for it without his fault. I could see number of customers in queue for the same issue.