How to get my old disk back that contains personal data?

I was not able to power on my MacBook Pro 2015. It was getting stuck on the Apple Logo. I took it to the Apple Service Centre, they diagnosed it and replaced the SSD.

The kept my old disk with them that contains my personal data and they are refusing to give it back to me. What are my options? I am sure there are ways they can still access the data. Are there any data protection laws for replaced disks from Apple's Side? Should I be worried?

I'd say don't worry.

Apple have a reputation to uphold & allowing customers' data to leak wouldn't do that reputation much good at all.

Assume they will safely recycle it.