Lot polish airlines - Refund has not been made

I booked a flight ticket in September **** from New Delhi to London Heathrow.
I was going for my studies in the UK.
Unfortunately due to some issues of delay in ATAS certificate from the UK govt.
I couldn't make it to the London at that time.
I explained everything to the polish airlines on their whatsapp.
They said refund will be issued after ** working days.
I waited and now it is more that ** days.
They are saying that they have intiated the refund on ** th Oct but nothing has been reflected in my bank account till date.
Even bank also checked everything and said no transaction has happened on that day.
I have to book another flight ticket and I have kept this refund amount to do the booking again.
But they are not giving me the refund.
I am left with no time now.
And the amount is not that small.