Mahindra and mahindra Company - Car booking refund not received after cancellation

Let me summarise on what happened in August ****. On **th of August ****, I booked an XUV *** online and used my AMEX Card for booking. I realised my card was debited twice . I raised a request with AMEX who promptly raised one charge as a dispute and reversed it. I still paid AMEX booking amount of RS **,*** as booking amount for * car. This was in August ****.
Over the next * months calls I have received calls from Koncept- Mahindra dealer that the booking is confirmed and a tentative date of delivery in **** was given..
As per the latest response they are claiming that the refund needs to be taken from AMEX. I have checked my card statements. Amex is not at fault.i have paid Amex ***** initially in Aug ** and the money would have gone to Mahindra. Now the refund needs to be paid by them.