decrease

Hello
which verb do you use in German for "decrease" in the sense of reducing/decreasing the weight or quantity of packages to collect?
For instance, if you advice 1000 Kg and then you must inform that you have only 300.
Will that be "abkürzen, reduziert....?" My try was "wir haben die angemeldete Menge/das angemeldete Gewicht reduziert"

Thanks
Ana

If I understand the context right, you could tell your customer:

Leider haben wir die bestellte Menge auf 300 kg reduzieren müssen.