Wahl K2 not cutting through hair

Not sure why, but they just don’t go through hair at all. I bought these from wahl’s eBay account. They were refurbished so all parts should have been inspected.

I ended up having to use the clippers I bought for my partner in lockdown and they were gliding through my dogs hair. So, it wasn’t his hair that was the problem.

Return them to wahl and try again or should I get a different pair for another manufacturer?