By paying the extra 750 DKK your total deposit paid is 2.000 DKK, which is the requested total deposit after 1st of July 2020.
The deposit is a lump sum paid once. The language school confirms your payment by letter, enlisting you in an appropriate class.
You will have the deposit refunded, when you have completed your Danish Language Course. The refund takes place within month after the completion of the Danish Language Course.
You can read more about the deposit here