State tax filing

That article about CA is horrifying b/c that is my situation. I'm a screenwriter in GA. And in any given year I can write projects for sometimes 8 states worth of clients.  But CA sent me a letter about one 1099 from 2017 and I'm still waiting on their answer. I had to pay the $50 for the extra CA download on the old taxes. And it shows I Owe CA nothing,  but I have the feeling 2019 changed their definitions but Turbo tax hasn't necessarily caught up with that. So even if TT says I owe Zero (which in reality I think that's exactly what should be due!!) When I lived in CA I paid CA my entire state tax bill no matter what state my client was in and CA didn't mind then. So why do they want to collect our money in reverse when we don't live there anymore?? It's insane. And if every state did that, some of us would be filing 8+ state tax returns a year. (Even just selling on amazon or audible, their 2 parent companies are different states. Amazon is WA and Audible for selling audio books is NJ which was on the 'double taxed' list posted above. So for that 1099 from this year worth less than $600 I'm also supposed to file in NJ???) B/c yes they sent one anyway even though it was under $600.

 

CA sent me a notice in August saying "we got your tax return" and we'll let you know your bill and fees / fines. But do they charge me interest on how long THEY are taking to look at it? (Even if my forms say I owe zero, I have no doubt the broke state will find a way to charge me on income I earned from home in GA)  

 

And a question... if Double Taxation is illegal... how do they determine how much of the income GA is allowed to tax vs. CA? I can't see GA thinking they are owed nothing for work I did here for  CA client. But it seems like how CA is working they think they're owed everything on that 1099. How is that fair to the state you live in?