Due amount

Hello Community, after I calculated the fee of one student and the student dropped a subject I only returned to that student the 66% of the amount, I have my due calendar split 35%, 35%, 30%. Before the student dropped:

By Due Date --Due amount

First date 9,660

second date 9,660

third date 8,280

Total amount=27,600

After the student dropped, it only considered the first, :

First date 5,106

second date 9,660

third date 8,280

Total amount=23,046.00

I want to know why and if there is a way I could do it, so it takes the 23,046 and split it on the three due dates, something like the example below:

35% First date 8,066.1