So sorry this has happened, OP. If you were in two minds about leaving, I'm sure you're not now. He's showed his true colours and then some.
You can get an advance from Universal Credit to tide you over until you get your first payment.
Here's the link for the form you need to download to register your interest in the matrimonial home:
www.gov.uk/government/publications/notice-of-home-rights-registration-hr1
It's pretty straightforward and will save a few quid in legal bills if you do it yourself. The notice will stop him doing anything dodgy with the matrimonial home, eg renting it out, remortgaging or selling it.
I'd also speak to Women's Aid and see if it is a criminal matter for him to close a joint account and deny you access to money that you are legally entitled to. Report to the police if so. Do you know of any other accounts he has that he might have transferred the money to? Or can you check the transaction history on the online account to see if it gives those details?
When you speak to a solicitor, make sure you ask about your rights to this money. You'll need funds to rent a property (unless occupation orders can be granted for emotional/financial abuse as well as DV).
Someone who's knowledge is more up to date than mine may know if financial abuse gives you rights under homelessness legislation in the same way as DV does. You may be able to get help from the council where the matrimonial home is, if that's the case, but that's a bit of a long shot.
You've been incredibly brave in taking this step. Your STBX has really shown his true colours, and not been very bright about it. He's left a lovely paper trail.
In the absence of a "handhold" smiley, have a
to calm your nerves. Good luck.