Fault at your backend servers. Either your Local Vendor needs to reset there machine configuration or there can be some configuration issue at Backend servers, You can contact Customer care by Call or Visit nearby Higher BSNL Authority member to get it fixed for your connection.
This issue occur in my State 'Himachal Pradesh' which got fixed after 1 week.
Issue : Optical Fiber got Cut by some 'ISP' (you know who do it) and it took 1 week to recover the fault. So, It can be some fiber related issues too.