[Resolved]  BSNL Broadband — bill was too much high

i have get BSNL broadband connection on 21 dec2008 for 750 home unlimited plane .and in jan 31 2009 i appilied for plane change to 250 home plane the officer recieved application and say that the plane was change from feb1 2009. and then in afternoon they call on my bsnl telephone no.[protected] that they were unable to chang my plane because i have take bb on dec so plane cannot change .then in feb2009 the plane is 750 home unlimited .and then in mar2009 they were change plane without notifing me so i had use bb as 750 unlimited plane and in 16 april 2009 bill was came with post then i know what the bill is about 49000 so i complaint to bsnl office but they not responding me and told that your plan should change in march as 250 home plane as you given the application on 31jan 2009 .how they can change the plane on my rejected application . please help me and give any idea what to do.
thanking you