Domoticz reading differ from Supplier data?

[Draakje]

Hi all,

I was wondering if someone could clarify the following for me:

I just receive a pdf from my energy supplier (Energie Direct) which contains the consumption for August and September. (01-08-2017 - 30-09-2017)
When I compare this data with the data I have within my domoticz I see a difference in electra usage for about 40kWh.

How can there be a difference?

the data shown by the supplier says I have used 541kWh and returned 557kWh
Domoticz tells me i have used 503kWh and returned 517kWh

The gas usage is correct (39m3 vs 38m3 )

Anyone any ideas?
Should I call the Supplier for an explanation?