Hi Fiona,
I've checked with William, the managing editor of Petster Magazine. According to him, the magazine's new issue for the year is not out yet (they had a pause in publication earlier), so that's why you have not received any issues.
You can try contacting William at the contact details here:
http://www.petstermagazine.com/contactus.html
Better to give them a call since you had problems emailing them.