from your ip profile i would think you are a good distance away from your local cabinet But the estimator knew that. The estimator can be wrong, but shouldn't usually be double the attainable value.
Probably best for the op to call service in India, or contact the mods at: http://bt.custhelp.com/app/contact_email/c/4951
(Once again it's a shame that Openreach hide the modem information that would make it easier for people to identify issues more precisely themselves or with a little forum help.)
Thanks for all of the responses and links. I've now emailed the mods, so I'll report back when I get a response.