Nothing mentioned about the promotion!!!

I bought 2 tyres Michelin Primacy 3 which happened to be on a promotion but I was unaware. Buy 2 or more and you get a laptop bag. Unfortunately I did not get anything. By chance, I happened to see on the website this morning (22-Dec-2015) that there is a promotion currently but when I bought yesterday (21-Dec-2015) nothing was mentioned whatsoever. So, I phoned today and they said they gave me a discount and with that there is no bag. If no discount, then you get the bag. However, the terms and conditions on the website don't mention anything about that. Nobody informed or briefed me about anything at the time when I was buying. It is so disappointing and unprofessional that nothing was mentioned to me about the promotion and I had to find out the way I did after I have bought already.