Orange PAYG mobile?

I've had two text from 'Orange' saying that I can get a free text for every text I send for the next six months if I reply 'yes' to them. the number given is 1164. I have emailed Orange to ask if this is genuinely theirs or is it a hoax but whereby if I reply, it costs me �1 50. As usual, orange haven't replied yet. Has anyone else received such a text and is it genuine?