O365: Calculated column needs to calculate the difference between two dates but exclude Sundays

I am currently using SharePoint O365 custom list with a New Responsive Form. I am looking for a way to utilize my calculated column to calculate the difference between two dates, but to exclude Sundays from that calculation (as these are considered exception dates). I also need to be able to reflect the difference on my form as well.

Column Calculation so far: =[Completion Date]-[Received Date]

Form Variable Formula so far:  dateDiff("totaldays",[Form].[Received Date],[Form].[Completion Date])