BB Curve :: Stop Auto-Deleting Text Messages?

I've spent so long googling and I've made exactly no progress at all...!!- Problem: my blackberry only keeps text messages for about a week before deleting them- Phone type: It is a blackberry Curve 9320. It seems to be on OS 7.1. I got it around the middle of October 2012.- Also worth noting: unlike most people I've found online with this complaint- my call logs aren't being deleted, and are still intact all the way back to the middle of October when I got the phone.- Also, emails aren't deleted after a week, they perhaps linger for as much as a month before vanishing.

(I don't care about those as much because I can access them other ways, whereas texts I can't)According to various googlings and also questions on here, this is most commonly due to lack of memory, therefore they suggest that you check your memory status and then free some up if required.- When I go into device and status information it tells me that my free memory is around 133602256 bytes (which I believe is in the region of 126mb?). Does this count as a lot or a little? Could this be the source of the problem after all?- Similarly when I look in memory use under media it says 'built-in media storage 96% free (30.4mb)' and 'media card storage 95% free (1.7gb)'The other obvious thing which I've checked (and initially thought had solved the problem but it hadn't) was 'Message display and actions' where I've had 'days to keep messages' set as forever but it doesn't seem to have made a difference.Am I missing something really obvious? How can I get it to keep my messages for more than 7 or 8 days?