lol you dont use a SD card as the phone shuts off? lolol
have you tried upgrading the firmware?
Then asking for a replacement?
tried a different brand of memory card?
and to answer the main question:
1.2gb? the total internal memory shown should be around 6gb, and this memory cant be eaten by the blackberry unless you have things stored in there. seriously, upgrade the firmware.
I think OP means 1,2GB left memory ( 5GB already saved before ) ...
Agree with Nah Uhh said , check hidden files/folder...
App > Files > Files Folders > Device > BBmenu > Click Show Hidden >