If you don't claim the offer at the time of your first deposit, you can do so at any time within 30 days of registering your account. Simply log in to your account, go to the Account menu, choose My Offers then click Claim Now for the relevant offer.
There are several reasons why bet365 accounts can be restricted, including matched betting, unreasonable betting behaviour, GamStop (self-exclusion), and exploitation of bonuses.