your call dates are in fact timestamps (non integer / having a fractional time part) and are just formatted as dates.
Try to load the dates without time information e.g. like:
LOAD DayName(Date) as Date,
instead of Date as calculated dimension.
hope this helps
First,choose your 'Date' as dimension,and in expression use 'sum(calls)' ,count() will give you the frequency and sum() will give you the sum of that field and yes after all the result will get a Group By according to your dimension. So,easy solution for your query make date as your dimension and make sum() or count() according to your requirement in expression.