I just had an incompetent Arborist prune my Green Giant. For some unknown reason he cut 4 branches totally off leaving a huge bald spot front and center of my row a arborvitaes. They claim it will grow back by next year, but I do not believe this for a minute. See the picture of the damage they did after I have been growing these for 7 years. And would anyone out there know why a "professional" would do this to a tree? I am just furious and cannot wrap my head around it. I think it was just plain malicious.
Those branches will not regrow - growth buds on these trees are at the tips of branches, or along the green branches, but not on the trunk or on old wood. Although not exactly the same situation, the answer contained in this thread https://ask2.extension.org/kb/faq.php?id=404019 should be useful to you:
Coniferous plants form buds only either at the tips or along the green growth part of the branches. The older wood with no green growth, closer to the trunk, has no buds to regrow. If you prune a conifer branch into the old wood beyond the green growth, that branch will not put out new growth or grow. This can leave a blank spot in the side of the plant. If cut off the top of a conifer like your arborvitae the only new growth you will have will come from the green horizontal branches.
On your arborvitae trees the upright shoots from the green parts of the horizontal branches will eventually grow out and up vertically to fill in the top open area of the arborvitae, but it will take several seasons to see . The cut-off top will not regrow. Conifers put out new growth yearly, so next spring you should see the top start to fill in. Keep in mind that if the horizontal branches are typical and only have green growth on the outer foot or so of the branch, the middle of the cleared spot may never fill in. Old wood will never form new growth.
I don't know why they saw fit to remove those branches, perhaps they broke them by accident initially, but you are justified in being cross about it, I'd be absolutely furious - the best you can hope for is the surrounding green branches will eventually bush out more and cover the bare part of the trunk that is, currently, highly visible. It seems they have not provided any explanation for what they've done, but unless they can provide a good explanation (such as rot or something) I would be asking for compensation. And never using them again as well as leaving a bad review anywhere you're able to to warn other people.