No response on email and called and are asked to hold-on for 15+minites

I had a settlement letter obtained on 21 Dec 2017 for account ********** 1117 and was dated till 26 Dec 2017 and it could only be settled on 27 Dec due to public holiday on the 26th Dec 2017 but on 29 De 2017 another installment went off on my bank account.

I called them on 22 Jan 2018 and was asked to forward proof of payment which I on the same day did. I called on 25 Jan 2018 and was asked yo hold-on which I did for 15+minutes until my airtime ran out, they fid not even call back and i am struggling to contact them via email, keep returning undelivered.