kaplan University they re charging me for a semester that i did nto attend to, becuase i dropped it after the second class fort laudardale , Florida

I went to kaplna university online for one semester, and the classes sucked. The teacher never actually tought anything we only discussed our reading assigments.  the second semester i decided to not continue and after the fist class i called the school and told them i was droppign the semester, they told me no problem, and since i dropped before the third class i was not liable for any charge. a year later i start getting calls from a collection agency saying that i didnt pay for a semster now is been over 4 years and they started calling again They charge people for classes they didint even take. what a rip off