StashFin — even after paying emi, again auto debited the next day

Address:

Mehdipatnam, Hyderabad, Telangana, 500028

I paid rs.8360 as monthly emi on due date 5th may, again on 6th may stashfin auto debited rs.8360 from my account. How it is possible.
When i raised this issue on chat, they are telling that it will be adjust in the emi of 5th june. It is fixed amount decided to pay monthly as emi including interest rate. Now if they are collecting (Not refunding) one month back then they have to pay the interest on it or refund immediately in the respective account.
3 months back also they did the same thing. Now it is second time and it is not acceptable at any circumstances.
Please find attached the docs for reference.
And second issue, i paid the emi on due date, so there will be no late fee, but they are charging rs.500. How and why? I can't understand.