Consumer Redressal

Dear Sir, I have booked a flat in Bestech Grand Spa Park View Sector 81. Bestech is asking for interest on a demand letter they did not send. On 20 Nov 2013, I received a letter dated 1 Oct 2013 (with 25 Oct as last date to pay). I immediately notified Bestech CRM about delayed delivery but they claim they sent me email on 3 Oct and demand letter on same day, which is NOT TRUE. I asked them multiple times to provide Airways Bill number of the courier or if they made a reminder phone call. They do not provide any evidence for either. They only show me an email in their out box which never reached me. So, out of 3 means of asking me for funds - physical letter, email and phone call, they say only 1 was done (email) which never reached me. Now they are asking for compound interest and despite multiple requests they are not willing to settle. This is causing great agony and mental pain. Please advise how do I lodge a formal complaint. Regards, Ashish Jain