Q.Holly bushes
My two holly bushes, newly bought last spring, lost all their leaves over the winter. What caused this, and will I get new leaves?

There is a possibility that the leaf drop was due to Holly Leaf Blight, or even Scale insects. Both can cause rapid defoliation.
Clean up any dead leaves and dispose of.
If you suspect disease or pests, treat as the articles recommend.
You will need to wait and see it the shrubs began to leaf out.
https://www.gardeningknowhow.com/ornamental/shrubs/holly/diseases-of-holly-bushes-pests-and-diseases-damaging-holly-bushes.htm
https://www.gardeningknowhow.com/ornamental/shrubs/holly/leaf-scorching-in-holly.htm
https://www.gardeningknowhow.com/ornamental/shrubs/holly/