Refund for Service not provided

Dear Sir,
I am a user of Airtel Prepaid sim card with phone no. 9729209490. Today I checked the recharge plan of 3G internet. It was showing RS. 264 4GB 3G/4G for 27 days.

I did this recharge using net banking. But the Service not provided by Airtel.

When I checked with there customer care executive, he said that this offer is for 4G sim and set only. I am using 3G sim and set.
I requested them to refund the amount but denied to refund saying that this is not possible.

Please help me in getting refund of service not provided by Airtel.

Also they should clearly indicate the offer valid for 4G sim cards only.

Please help.