Why the fee changes when the fee did not change

Tuition is set in the destination currency; the family pays in the home currency. If the home currency weakens, the fee in the destination currency is untouched and the amount leaving your account rises anyway.

Over a three or four-year course this is not a rounding error. Currency pairs move meaningfully across multi-year periods in both directions, and the direction is not forecastable by anyone — which is precisely why it has to be planned for rather than predicted.