Need an excel sheet created to calculate past due amounts and interest and penalties -- 3

Hi. I ok on excel, but just hit a brick wall trying to create a sheet to calculate compounded late fees and yearly interest on about 14 accounts that are 10 to 14 years behind in monthly payments. I need to have an excel sheet that calculates the current balance for principle, late fee and interest as per: accounts are 14 years past due. monthly amount due was one amount($35) and changed to a different amount ($50). I need to be able to enter the original date of non payment, the monthly amount that should have been paid on that date, the date the monthly amount changed and what that amount changed to, the end date that the whole period should be calculated to. 10% penalty on deliquent amount after first 10 days of non payment. 12% interest per annum from date of deliquency until paid. the attached image is the contract verbiage defining the penalty and interest. Does not need to be fancy or full of graphs and such. Just need to get total amounts. creating separate sub excel sheets with amatrozation tables would be useful, but not a requirment