Employer demanding unpaid overtime and not renewing contract due to complaints about illegal shift changes

Recently, my employer changed shifts for another employee over WhatsApp without notifying them and I ended up working an additional hour of unpaid overtime. I complained about this in writing, saying that in the future I would not remain at my post if such shifts changes were made in the future. I recieved some nonsense speech about teamwork and my boss wrote that, "If you have a problem with staying an addition hour, you need to come talk to me personally." I was not compensated for this additional hour.

Recently, he decided not to renew the contract of a fellow employee and highlighted the fact that he complained and working a 16 hour double shift with only fours notice. This was unfortunately not in writing.

I work as a receptionist at a hotel, and some of my coworkers seem to recognize that this kind of thing is wrong, but don't want to expend any energy asserting their rights. On the other hand, I am a highly vindictive person and find this type of behavior morally outrageous. Especially because the incident is not isolated and I could write a longer list.

Can you help me understand my rights, and how I could make my employer's life more difficult?

Thank you. Merci. Dank je wel.