Email them and ask them nicely if they will replace your expiring credit with a 12 month customer goodwill credit. Evangelists at tech companies can give those out like candy.
They offered an option to withdraw the money (Paypal) but I was trying to show support and left the credits there. I won't make the same mistake again.
So I guess I answered my own questions. I am being immature about it, like these companies complaining that Twitter cut API access. I should have known better.
It seems a little silly if they give such little notice that I'll just move elsewhere. I feel quite a bit betrayed by them not grandfathering in customers for at least a reasonable time (like the 12 month period they have on their new credits).