Making things worse :-) To attempt to recover a reasonable appearance after this type of malpruning, it is best to allow the tree to just do its own thing with regards to the top growth. At least for a couple of seasons.

It should want to produce from the existing branching (or what's left of it) and fill out on its own. You may need to thin out excessive shoots emerging from the cuts so that they individually harden off properly to provide support. And continue to clean out any dead wood or stubbed cuts. And remove the shoots from lower on the trunk - I prefer to just rub them off when they are still small.

It may be helpful to provide photos if you need more specific advise :-)

How coincidental...

Thirty odd years ago, my father bought me an Acer Palmatum Dissectum. Every Autumn I dead-wooded it and consequently it's a gorgeous specimen; or at least until yesterday it was. I am laid-up at the moment after knee surgery, and my daughter-in-law, in an act of kindness, decided; unasked, to clear up the patio which was becoming weed infested. At the same time she 'pruned' the maple, thinking that it's weeping habit was merely overgrowth. Now my pride and joy looks like a lone Acacia tree on the African plains. At 74 years, I wonder if I shall live long enough to see it in its full glory again.

Would similar treatment to the above help the shrub survive?