Hi LZ
There are 'no rights' for you to be offered a second extension. People have been awarded two or three - but you were a little unwise to leave it until the last minute. Please ring again ASAP and hold on until you get through - it could be up to an hour or more. What you don't want the DWP to do is to cancel your claim because they think you haven't returned the form. Now, they should give you a little extra time - but you never know how long that is. Not trying to scare you, but that's the reality of what can happen.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
