Has anyone gone to work and been told they abused system for being off ill even with a sicknote?

Work issues. This can happen. People will say what's on their minds, and sometimes without sensitivity to others. Don't worry about it. What people think about you is their business. You just stick to your principles and values and move forward. If someone doesn't approve, it's ok. No one gets approval from everyone. If you're unhappy with people at work, it might help to focus more on the work itself.