South American Cranberry from seed

[Medbury Gardens]

Ive tried to grow the South American Cranberry but find it doesn't like the odd heavy frost i get here,the first two plants i brought died so i brought two more,had a good crop in its first season so i tried to grow some plants from there seed with the idea to find some stronger seedlings able to handle this climate,but none came up in the autumn as well as in spring.
So ok what i'm i doing wrong,ive tried to Google the question but couldn't find any info,lots came up for the North American type though.
Anyone have any ideas or links ....please,i so want to crack this one