Seller refusing the Refund of advance amount which we are not willing to buy

Hi Sir/Mam, We have decided to buy the flat from the apartment and made a notary register by paying the advance amount of 10lakhs with 2months time period for registration and we have decided to make a sale deed but now we found that there is some document issue in their property and we have decided to drop the plan to purchase that flat. We informed clearly to the seller and asking for the refund but they are claiming that there property is valid with all the documents and no issues with it and now they are refusing to return the advance amount and they are already started to post the property is available for sale in online platforms but still the sale agreement is valid for 1.5months and they are refusing to return the amount And also claiming that they will return the amount after deducting compensation that it is made cost loss to them like that they are claiming and also will return after the 2months they are claiming it. Can you please help and advise me here how to proceed this legally to get full refund. Thanks