Settlement payment STILL not allocated after 2 weeks!

I made a settlement payment to Edgars on 31 May 2019. The payment was done directly by FNB to Edgars using the payment details and references as provided. The proof of payment was sent to Edgars, but to date, they still have not allocated the payment and on top of that, are charging me extra interest for unpaid instalments. The latest email from Edgars, states that I must AGAIN send a full proof of payment in order for them to allocate the payment to my account. Why??? When the payment was made, the exact reference number and details were used as indicated by Edgars themselves! I cannot understand the holdup or Edgars reasoning for witholding the funds AND charging me extra when all I wanted to do was pay the account in full. Disgusted with their service!