Airtel — 4g hotspot

I requested cancellation of my 4g hotspot. Customer care called me and asked me not to cancel and that they would give me a plan of rs 450 with rs 300 loyalty discount. I was assured that my bill would be rs 177 per month. However a different plan was activated and rs3807 was deducted from my account. The call was audited and airtel admits the mistake. Now they are not refunding my money. Please help. This has been going on for 1 month now.