Nedbank Home loans misled us

My husband and I have a bond with Nedbank since 2008. We bought a house in Danville throuhg an agent. We bought the house for 502 000. Its an old 2 bedroom with a kitchen and a bathroom with a garden cottage with 2 bedrooms, shower and a toilet. We have done some minor changes in the main house, like putting ceramic tiles in the whole house, putting kitchen cupboards etc. No changes have been made in the garden cottage. This Year (2015) when we wanted to sell the house for 650, Nedbank does not want to fincance the buyer because they say its risky, and complain about the materials used to build the cottage, BUT THEY SOLD IT TO US LIKE THAT. They keep saying they made a desktop approval, Now we are stuck with a house that Nedbank says it is overpriced, but they made us buy it that expensively. They are ****** who will stop at nothing to frustrate people. We no longer leave in Pta but we are stuck with a house we dont want. When we go to the Bank, we are told you can only email and call home loans section. This is their way of avoiding problems. Why cant they give us an address to go to so we can sort this out once and for all. They keep referring us from 1 department to another.