Refusing to hand my parcel to my client

I have booked a box from joburg to kroonstad through pudo service. They collected my box from the locker in cosmo city mall to kroonstad, when it reached kroonstad they are refusing to let my customer collect the parcel say it is too heavy.

Only they realizing that it's too heavy they want R360 on top of the a booking fee that I have already paid. when it reaches a destination, why did they collect it in first place, why at the destination are realizing that the box is heavy?