You don't have to ask for extensions. If your club is doing well financially and you fill the stadium on a regular basis, the board might decide to expand. But you should get a mail/notification when they decide this. Did you go on holiday when they decided...?
Well, then it just sounds strange...
On the other hand, it is a good thing afterall. More income on matchday for you. Would've been worse if the capacity suddenly decreased for some unknown reason...