Jen
Is this NatWest/RBS?
It could be there was a fault with the card or the banks IT system has noticed irregular transactions. The banks systems have in-built security that can automatically stop cash withdrawal and retain the card when next used.
If you contact your bank on Monday, they will look into and order you a new card. You can obviously still withraw money over the counter, with a cheque. But I would suggest that you take other forms of identity, credif card, driving licence.
Hope that you manager to sort this matter out and that it is not anything more complicated.
Huckster