Lenovo — BTC offer not provided by company

Address:

Ahmedabad, Gujarat

I have purchase Lenovo z51-70 laptop on 15th Aug 2015, They have an offer BTC till 21th Aug 2015 on Term & condition page, while on FAQ (http://lenovoservices.net/FAQ.aspx) page it says registration last date is Set 30th 2015.
When I have tried to contact them they told me this offer is already expired on 20th Aug. 2015, Now they are not responding me.

If last date was 20th Aug. 2015, then they must mention some where. but they didn't

I want to claim this offer for my laptop but they are refusing this one.

My mail id is :[protected]@gmail.com

How can I get this offer? Please suggest.