Terrible customer Service & Accounts department

Very disappointed in your service Edgars! I've had my account with Edgars for the past 7 years and I've been a loyal customer. I recently received my latest Edgars account, which I have been faithfully paying as indicated. On the latest statement, they requested that I pay an installment of 28% my total balance owed! I sent an email to the accounts department to query this. Still waiting for a response. When I contacted the call center the lady could not give me a formula or explanation. She said its system calculated and that I must pay. Please clarify why you want me to pay 28% of the total account balance in one payment? Should this not be calculated over the 6 month period or at least take the latest balance in consideration? Could someone please explain this to me or at least look at my account?