Lewis stores opens a new account for me when there is a existing dept

I settled my account with Lewis through fnb last year and in November I went to another branch to buy a new fridge and bed of which a new account was opened. To my surprise this year in may I receive a call from the other branch where I bought my couches and TV (the items that I settled earlier last year) to tell me that I owe an amount of R4000 something and when I asked how that could be I was told that when I settled the account there was an outstanding amount of R1000 of which I was never told about till this year, I mean it's not my first time settling Lewis through a bank, the settlement amount is always accurate. I don't understand how a new account was opened when I still have an active account which was owing because I believe they use one system, they should have been able to pick this up in November and bring it to my attention. I am very disappointed in Lewis stores as I have been a very loyal customer. All my furniture is from Lewis and I have been happy with them. I sent a complain to their complaints department in May and June and still haven't received any feedback from them, I will not let Lewis ruin my credit record. If they fail to resolve this issue, I am taking them to the ombuds man. I will not pay this amount because according to me this account was fully settled.