Well thats great whitty, now you know the hold up on your file. Start getting the proof so you can send it in as soon as possible. You can include things like the rental agreement/lease if both your names are on it, bills sent to both of you at the same address, joint account bank or credit card statements, if you dont have these at least show you both recieved correspondence to the same address. Good luck!
Oh if you provided these things before you should have your wife indicate to them that this info was already provided. It could also be that they did not deem what you sent as enough proof and they want more. IDK