poor admin and account administration

I used LDS couriers services since march 2019. Had no problems with collection, transportation and delivery of parcels . Admin and accounts is a disaster. You provide them with detail (sizes and weight) and desitination of the parcel. They provide you with a quotation for the collection and delivery of the parcel. Customer pays the quation fee and LDS collects and delivers the parcel without any problems. The problem is when you get the monthly statements and accounts. They charge more than the quoted price. You pay the extra charge and provide them with the proof of payment. LDS accounts do not read their customers emails or update the accounts. I have sent proof of payment for one specific shipment more than 8 times but the amount is still refkecting outstanding on my account. I have phoned , emailed , and provided proff of payment in order to get my account updtated. Every month I get the same statment and account still showing that I owe them money for my first shipment paid in March 2019. I am now gatvol because they are not reading my emails or updating my account. This is unacceptable. It does not help to have a good delivery service , but poor admin that double charges you for your shipments. I do not know how to get my account updated because sending them emails does not work.