Edgars trying to ****** money from me after payments have been made

my last installment was due on the 01/04/2019 owing R748.40 total due R748.40 i made payment of R748.40 i get an email for May stating that i owe, i made an enquiry and sent proof they respond a week later advising me that i owe and over and above that are charging me what looks like double for a "late installment" firstly my installment is not late its paid up to date there was no balance of what i am owing, 2ndly you want to charge me also most double on the day that you respond to my query and you are the ones that took a whole week to respond, even if i am mistaken which i am not because i have been waiting to pay up this account you people respond a week later and want to now charge me for a late payment? sounds pretty much like a ******* hey, further to that i have compared my previous months statement, your statements NO LONGER shows future balances just is what is due for that month, sounds pretty ***** to me! i require a full statement for the last year of my balances what i have paid and my totals due and you will not charge me anything for late payments as is it not my fault that you are being ***** with your statements and respond to queries late!