OK, it seems i must have confused the whole thing. I managed to just solve it

SELECT MeterID, COUNT(TimeStamp) AS Count, SUM(WattHours) AS WattHours, MONTH(TimeStamp) AS Month

FROM BillingHistoryvMData

GROUP BY MeterID, MONTH(TimeStamp)

As i wanted to count the timestamp column by month and them sum the months watthours.

Not been one of the best weeks regarding concentration, pregnant partner.

Sorry and thank you