Hi Alexander,
If you have enough samples, don't get any more. While it's good to have extras, your situation is not a good one and you've highlighted that you are scared.
I would get in contact with your student union about your options regarding reporting harassment claims. The professor is abusing his power and is liable for his actions, especially as you are a postgraduate student. As to whether you should go to the department, I don't have an answer, but that might backfire on you...
Go to the student union, they will be able to help you out on your next options. Also seek counselling at your school, they should be able to help you, as well as if there is a safer communities (or something similar) unit at your campus.