My Premium Cannot be traced

I joined med shield effective from December 2015, my first debit order date was the 15th of December 2015, Which went through successfully, I then deposited my premium for January 2016 on the very same day ( which the EFT details I received from them, this is because I knew I wouldn't have money in my account on the 15th of Jan. What upsets me now is that they are not able to trace these funds, I have made a lo of attempts to have them resolve this but they still haven't, instead they still debited my account and had the nerve to send me an email saying the debit order has been unsuccessful, This has a negative impact on my credit score.