More important than the loss in volume is going to be the possible contamination. I am unsure how your sachet arrived, how it was packaged etc. If the sachet was opened somehow it may no longer be a sterile compound.
Unfortunatley I do not have any tricks as to how to go about attempting to purify the remainder of the sachet, but I'm sure there are many in this forum who know how to.
As far as contacting the distributor, go ahead, they should be informed but they will probably do little in terms of compensation.