Are these sentence correct?

[Annecy]

This has reference to the overtime payment issued for the maintenance department for the last month dated .
Upon reviewing the employees overtime, we found that some discrepancies in the calculation of overtime that you made. Did you the change the calculation of overtime, because all employees' payment are having same problems. If you already changed the overtime calculation, you should have announced the changes before distributing their payments so that we could have avoid this kind of mail
Also, note that I asked your accountant when I received the overtime payment for the employees because I got doubt one of our employee's overtime then he replied that everything was correct and accurate. But, even if you calculate with your new overtime rate there will be a shortfall in his payment.
Previously, we were receiving overtime payment at hourly rate. (normally, hourly rate calculate as daily rate = monthly paid/no. of working days, hourly rate = daily rate/normal hours of work). How did you change the calculation? please clarify on this issue.

[bertietheblue]

This has reference to the overtime payment issued for the maintenance department for the last month dated .
Upon reviewing the employees overtime, we found that some discrepancies in the calculation of overtime that you made. Did you the change the calculation of overtime, because all employees' payment are having same problems. If you already changed the overtime calculation, you should have announced the changes before distributing their payments so that we could have avoid this kind of mail
Also, note that I asked your accountant when I received the overtime payment for the employees because I got doubt one of our employee's overtime then he replied that everything was correct and accurate. But, even if you calculate with your new overtime rate there will be a shortfall in his payment.
Previously, we were receiving overtime payment at hourly rate. (normally, hourly rate calculate as daily rate = monthly paid/no. of working days, hourly rate = daily rate/normal hours of work). How did you change the calculation? please clarify on this issue.

"I am writing with regard to [Month's] overtime payments to employees in the Maintenance department.

In reviewing the employees' overtime payments, [we – who? Specify] found a number of discrepancies in your overtime calculations which appear to have affected all the employees. Can this be explained by changes you made to the basis for calculating overtime?

If this basis was indeed changed, you should have announced this before making the monthly payments so that we could have avoided having to contact you in this manner.

In addition, please be aware that, upon receipt of the overtime payments, I made enquiries with your accountant because I had doubts about the accuracy of one particular employee's overtime payment. I was told that the payment was correct. However, even if you calculate the payment on the basis of a revised overtime rate there [is clearly][appears to be] a shortfall in the payment made to him.

[Previously, overtime paid to the employees [of our department] was calculated at an hourly rate - ? So it's not calculated at an hourly rate anymore?]. [(normally, hourly rate calculate as daily rate = monthly paid/no. of working days, hourly rate = daily rate/normal hours of work) – I'm not sure of the sense of this. Is this a comment or is this part of the text? If part of the text, please clarify]. Could you clarify why the basis for calculation has changed?"

Hope that helps!

[bertietheblue]

I can't keep re-editing but I thought I'd mention that there are too many 'payment's in the last but one paragraph of my version - I say that in particular in case jasmin165 is reading because,, only a few hours ago, I was suggesting that he/she avoid repetition of the same word over 1 or 2 lines. But I've done exactly that!