Enrolled at a US college for fall 2016 now do not wish to continue

I recently enrolled at a US college for fall 2016. I withdrew and now they are harassing me. Classes started on Aug 22 and last date to add or drop classes that is last date of registration was Sept 3 and last date to pay tuition was Sept 6. I withdrew on September 6 and came back to India on Sept 7-8. Now they are harassing me that since I've registered for classes I have accepted financial responsibility and asking me to pay up $14,893, that is the entire semesters tuition. They say if i don't pay up they will send my case over to a debt collection agency. What to do now. I neither want to get into any legal trouble nor pay $15,000.