My boss called me on a Saturday to let me know that due to financial reasons, I was no longer needed effectively immediately. Three days later, he send me a text about work issues. How do I respond?

The bigger question is why should you respond? Are the bridges burnt or do you still see yourself to have a future at that company? Do you still need that job or can you work it as an opportunity to hire you back? If he’s that desperate, maybe you can negotiate a better salary before agreeing to answer his query. Perhaps your contract states that you’re still obliged to answer these requests and you might want to do it out of professional courtesy, or at least until your final paycheque is in the bank. They’re trying to get more out of you for nothing, or at least hold you to ransom for a reference if you need one. But if you have no further obligation or desire to honour this request, then there is absolutely no reason why you should. You could even waste their time as vengeance for wasting yours.