How to truly estimate complexity?

I learned, (somewhat) used and taught agile for years. In theory it's beautiful, but I always connected sorry points to time blocks.

Now that I'm a CTO, I try to help our small dev to a better planning process, but we can never fully deliver a sprint, even underestimated ones. We think of points as something that takes around 2 hours, and I feel this is wrong, but don't know how else to do it in practice.

Also, we do not track worked hours in any way now. I always hated to do it as a developer, so I don't want to introduce it here. Is there any way to get an overview of the process without tracking hours?