Free texts for registering ??

[Osem]

I've never bothered registering my Virgin PAYG mobile phone and recently received a text from Virgin Mobile stating that if I did before the end of the month, I'd get 100 free texts next month. I'm no great texter so didn't bother but today I got a text from Virgin Media @ 789789 thanking me for registering with them and telling me that "we've just added your next lot of 25 free texts to any UK network for you to enjoy this month..."

I'm confused by this as I don't recall registering my mobile with Virgin Media and have never recieved 25 free texts before so what's going on? We've been on Virgin Media at home for years and recently stared taking advantage of the free VM landline to Virgin Mobile calls but don't think doing this involved registering my mobile with VM...

Can anyone shed any light?

Cheers as always.