ITC listing for 30 days late payment

I have an account with Edgars and since I opened the account until current date, have I never missed a payment on my account neither was it late or less than the amount payable. Payments was made ON or BEFORE due date of invoice! As of February 2015, Edgars ITC listed me for 30 days late payment. I have requested a letter stating that is was n mistake from their saide and it should be rectified. Today 2016/02/22 I am trying to arrange vehicle finance but unfortunately no Bank wants to approve my application due to the BIG mistake Edgars made on my Credit Report.<br> I want this issue to be resolved as a matter of urgency and my account should be closed and whatever debt there is should be written off! I am done with Edgars. Very unprofessional...