Please consider new time table in the attachment (Rental-1.pdf). I have revised this for easier understanding and also Thai description for your accountant.
Refer to Rental-1.pdf.
1. You have paid for 24 April - 3 June (just 41 days, 2 bills).
2. I'd like to ensure that I waived the rental for you by maximum 59 days (24 April to 21 June), more than your expected 50 days (24th April until 12th June = 50 days).
3. Your 41 days paid rental (24 April - 3 June) will be forward to the next cycle (22 June - 1 August, 41 days).
I also enclosed the last 2 receipts for your reference.