Sold bicycle

I found a bicycle that was on sale on their website, whilst I was on the process of making the purchase I was allocated a sales person(Mohammed). I then started liaising with him regarding availability of the bicycle where he assured me it was still available and processed request as per conversation. Monday morning another gentlemen called me and told me that the bicycle had been sold already and would be refunded. To my surprise they sent a refund note stating process would take 3 - 21 days, how is this my problem if they said the bicycle is still available? I'm now inconvenienced and need to pay for another bicycle I found elsewhere...