Dumb question, but Is your shield actually equipped? Sounds like it is on reading your description. You didn't mention what your health and stamina were when being attacked. Low health = low stagger limit and of course, you need Stamina to successfully block. No Stamina = no block. Lastly, what armor if any are you currently using. Unless you're running around naked with no food then it's weird that a Skeleton would stagger you.
Bone tower shield has block armor of 32/38/44 depending on upgrade level.
Bronze buckler is 16/22/28.
Troll does 60 blunt, 1* Skeleton does 37.5 slash (sword)
Neither one can fully mitigate damage from a Troll. I can see you getting staggered if your health and stamina are low.
A banded shield will be a definite improvement over both the shields you mentioned.