You should send a professionally drafted legal notice to them through an advocate. The notice should be sent to their corporate address via registered post, so that you receive an acknowledgement upon delivery.
Wait for 30 days for a response or resolution from their side. If you do not receive any relief, you may file a case with the Consumer Commission in your district. While you can handle this process yourself, it is always advisable to hire a lawyer to send the notice and file the case on your behalf.