Charged R372 extra for an account that was paid late by

I have an Edgars Acc for many years and have never skiped a payment or paid my account late.

Unfortunately this month I paid my account on the 7th of March,instead of the 4th. i was told to pay the installment due R426.56 plus R372.19 (amount overdue)? i refused and only paid the instalment which is R426.56.

I want to know what is going on, I am a pensioner and have a good track record with Edgars. Do you want me to close my account?

I emailed Edgars about this on 7 March and was told this query was sent to the accounts department but have still not received a reply!