I need Excel expert for calculating reducing flat/simple interest

I need a formula to calculate simple/flat interest on reducing basis for every month that the borrower deposits.
For example, 10,000$ are given at 2% flat per month for a inspection period.

Scenario one,
For the first month interest is calculated as, 10,000*2%= 200.
So if the borrower deposits 100 in the first month, next month interest should show up as, 10,000*2%=200+100(previous month balance)

Scenario two,
If the borrower deposits just 200$ in the first month, the interest for the next month would be calculated as, 10,000*2%= 200+0(previous month due)

Scenario three,
If the borrower doesn't deposit anything for straight 2 months.
Interest due for third month will be calculated as,
10,000*2%*3(number of months due)=600$

Scenario four,

Borrower doesn't pay for first month,
Interest due for second month will be,
10,000*2%*2=400
And now he deposits, 900$ during second month, effective balance should be 900-400(interest due)
And remaining 500$ are to be subtracted from the principal amount (10000-500=9500)
So now next month interest will be charged at 9500, which will be 9500*2%= 1900.