<human>: Warning: a bit of a rant.

Firstly, I was sacked from my old job under very shady circumstances. My "boss" even went to the wrong desk and nearly sacked someone else by accident thinking that person was me. 

It was a very large corporate-focused NYSE listed international company, and I worked in an office in Australia. I have a very broad range of specialised skills, I work in engineering design, but also do amateur computer programming as a hobby. 

One of the projects I was working on I managed to combine the two and was achieving some really good things. Unfortunately only a handful of people who didn't count could appreciate my work.

When I was 'made redundant', no-one was left to take up my old project, since no-one had the skills. Ironic really.

Fast forward 3 months later to now, I'm in a new job, and my old work are contacting me asking for help on the project I was working on. It's only little for now, like where did I save things etc, but I can foresee it growing to become a hindrance to my current job.

All I really want to do is tell them to get fucked and they shouldn't have sacked me, but don't want to take a hit to my professional reputation.

So instead I want to say that I won't help them unless I get paid, but I'm not entirely sure how to go about it. Do I wait until it becomes more than minor questions? Where do I draw the line? How much do I charge?

I'm thinking of saying that I will work for them as a sub-consultant, but my business acumen is virtually non-existent and they would eat me alive.

Give me a shortened version of the text
<bot>: Opportunity to work as a sub-consultant for my old work, but I hate them and don't know what to do.