Bad online experience and communication

I placed an order on the 20th February, order number: ***, one of the items I ordered did not arrive, I did an online complaint and they came back to me saying they emailed me to say no stock, I rep**** to that email asking for them to re send proof of that email because I did not receive it, I have had no reply. I believe the reason there is not stock is because they made a mistake with the price of that item and they are using an excuse about stock, that is false advertising, I have kept screen shots and proof of all the transactions so they can't deny it.