Unable to access MTNL BB since MTNL number changed


I have MTNL 199 plan for the last 2 yrs. It worked fine till 2
weeks back when my MTNL no changed. Since then I am unable to
connect to the net. Its only when I remove the receiver of the
phone that I get SOME net access to the extent the pages take
around 40-50 sec to load.As soon as i place the receiver back
on the phone the ADSL and PPOE light goes off.
I read some where about SNR Margin and Line attentuation.What
are these and how are they checked.
Please guide on how to restore my net connection.