Corroded to buggery, most likely, those tophats are shit. Molegrips are usually all it takes, if you can get either one out then you can tap the other out from the inside easily. Then order proper shock hardware and curse the name of whatever cheapskate specced rubbish to save about 2 grams and a pound, which has now landed you with a problem and a bill.
There’s all sorts of tricks you could use to remove one that won’t molegrip out, but tbh they’re also mostly tricks that a) you’d know if you’d done it before and b) will incredibly **** up your shock if you do it wrong. So I am inclined to say this is not the time to start.