Please contact the universities that you are interested in, and explain your perdicament (the ACT orginazation's website does not have any remorse if you are from a foreign country - they don't even mention what to do if you are from an international country. If they say you need the writing test no matter your circumstances, you can still take the SAT in November and December - abeit to late for Early Decision, though, but still it is better than nothing.
Sorry, I can't help greatly, but since ACT has very little presence outside the U.S. unlike the College Board it is very hard to find out what their procedure is like. Hopefully, you can still take the ACT without the writing section and be able to come over to the United States for your college education.
As I said before, try to contact colleges that you're interested in and see what they would do if they were in your shoes.