Will I need to repay for Invisalign? Or if it may be discounted?

I went through a full treatment of invisalign in 2015. I wore my final retainers for about 6 months and lost them and now my teeth have shifted back and I am wondering if I will need to repay full price to have the treatment redone or if it may be discounted? I was really happy with the result and am really bummed that they have moved back.