Disappointed

I bought a sink in June, when our builder came he advised us to rather take a drop in sink. So I called takealot and advised the consultant and she told me to return back the item and my account will be credited because I told her it's either we get a credit or we do an exchange because we want to buy another sink. Few days later we receive an email that the credit was declined because "it did not meet their criteria". All I wanted was an exchange we pay the difference but now they are telling me that they will send it back to me. The sink is nicely sealed as we received it when we bought it nothing was removed, the courier stickers are still there everything is still as it was and they are telling me about a criteria that was not met???