There's a difference between the government of the country in which you hold citizenship asking you to pay taxes, and a group of terrorists walking into your home and extorting money from you.
With taxes, you always have the option to move your money, leave the country and become a citizen elsewhere, or lobby to change the tax laws. And in theory, your tax dollars go to support government programs, which you have a voice in shaping or changing.
With extortion, generally you have no choice. You pay, or someone dies. Your dollars go towards whatever your extortionists decide to do, without any discussion. ISIS isn't your government? Tough. Pay up anyway, and it's none of your business what they do with it, or when they decide to come back around for more.
You can't compare the two. ISIS is not a government. They have no authority to collect money, and they're not using the dollars they collect for the betterment of the lives of people who pay them.