Definately ring them up and they take your details and send a voucher- either £5 or £10 .
I had some in summer and the pouches were swollen - i opened one and it knocked me sick - they said there must have been a tiny hole somewhere and air had gotton in . I got a £10 voucher , but have had one or 2 other problems and got a £5 voucher -sometimes you have to send them some unopened ones from the box to check.