Did you close the account manually or via the Switch Guarantee service? https://www.currentaccountswitch.co.uk

If signed up to the scheme (most are, including Santander), your old bank is responsible for passing on any deposits directly to your new bank account and the new bank is responsible for processing any transactions made using your old details. This carries on for, I believe 12 months.

I found the Switch Guarantee service to be excellent and believe it's a significant driver of innovation and competition in UK banking (which is far ahead of many other European countries in my experience).

My payees from my old bank were even transferred over to my new one.

(Current account = checking account to any non-UK readers.)