Just to explain a little:
The letter you got lists all the documentation required to process your claim. The warning about 7 days is to cover the fact that if you fail to reply or supply ANYTHING, they can close your claim without further notice as they will asssume you don't want to pursue it. In your case, if you are supplying them with othe stuff and telling them about your bank statements problem so they won't close the claim.
Presumably, the bank statements are requiredd to show your monetary activity over a period of time and to show you haven't moved monies out in order to qualify for JA. That is why sometimes a current balance is not accepted by them. Talk to them about it when you are contacting them this week.