So for the background I worked for a department for 2 years and in my field its considered top of the line work. But I also have other non related technical skills and developed a crucial scheduling application for them among other things. It saves their scheduling manager two weeks as it automates basically his entire job and integrates with the time clock system. I gave them very specific requirements for the amount of time I would need so they knew ahead of time. They did not compensate me for the last two weeks of work on this project and it was quite upsetting at the time. But I let it go and did not involve HR.
Through all this I dealt with employees being highly inappropriate, a lot of racism like tons of it, homophobia, and misogyny. Towards the end of my employment in this department I was really tired of some of these guys and how they were treating the women I worked with and I stood up for an employee who was being sexually harassed (putting sexually suggestive pictures of her around the office and men's urinals) and I was retaliated against for doing this because I wasn't one of the "bros". Our HR department did not help the poor girl and she was shit on for along time after for not playing along.
Over the next month or so I started getting blamed for a lot of problems with things that I didn't even work with. Mind you I had top marks on every review in this department and in every department before and I had never had a complaint. But then I started to get blamed for stuff I wasn't even involved with like failed projects or quality control.
Needless to say the harassment kept on and HR did not do anything about it. I started looking elsewhere and other departments were very interested at first but then I stopped getting communication. I got blackballed for a position I was looking at in another department and did not find out about that they had spread rumors about my professional work ethic. So I left and took my first job back at a 15k loss of income per year.
Before I left though I provided them with the source code and complete documentation on how to run every aspect of the application because I document my code extremely well. I'm also not an asshole and didn't want to make someone's future job harder.
But now more than two years later they want me to "make changes" but I do not feel like I am obligated to their department especially after the non payment, the pay cut, and the way I was treated. Also they have all the required material to do the changes themselves they just didn't RTFM the info they need is on the first few pages.
So I do not know how to go about this. I really do not want to help them after all that. I also don't want to seem like a shit employee either as I have been asked several times recently by my current department to move up into management because I am a consistently top performer.
But I also want to get paid and if I help them I most likely wont get paid either because its another department. It is a problem I have encountered in the past when my skills were needed by another department as soon as talks about paying for my time were brought up I was told they couldn't pay me for my time.
Also to complicate this my senior director is over both my current department and that department so I don't want to piss him off either but I still want to get paid for my work and I want to be treated fairly.
Additional info: It is all within the same company we have about 20k employees.