I almost dare not ask this, engine frozen, thawed, nothing is happening.

This is a call for help! I drive (drive???) a Citroen ZX Break, and I love it very much (have it????). 3 days ago I wanted to leave it on, but the engine gnawed strangely and didn’t jump on. Then my father and I dragged the car into the workshop to let it thaw and put better antifreeze in the cooling water, since the previous obviously had not done its service(-18°C). Today it was agreed that I could pick it up, but when I a When the workshop arrived, the owner told me that there was nothing to save on the vehicle, there was no “compression” anymore. It was probably something bursting in the engine due to the expansion of the ice. Now I want to know: What exactly can have happened? And what, if at all, can you do about it without changing the engine or buying another car? I’m a layman as far as KFz mechanics and the like are concerned, but I don’t think this problem is more cost-effective. I thank you in advance for all the answers, would be very connected if someone could help me.