My credit rating effected

My son bought a flat years back and I had to sign surety for him. He sold the place but due to the bad economic climate could not get the price to settle the bond. He entered into an arrangement with FNB Residual Home loans to pay off the balance, which he is doing per debit order monthly. In fact he is paying more than the agreed amount. I app**** for credit from my private banker and was turned down because of this home loan which is supposed to be in arrears. I enquired about this and was referred to Residual Home Loans which told me that the problem will go away if I paid off this account. This is unfortunately not possible for me and the more I argued with them that the loan is being paid off in terms of an agreed arrangement the more I am told that I should settle this account and my credit record will be cleared. I feel this is ************ on the side of the bank and it should be properly investigated.