Freeview boxes i cant seem to pick up certain channels?

I have a digihome set top box but I'm having a lot of trouble picking up many channels. I've only got bbc1 ,bbc2, bbc3 but no bbc4. Itv2+1, itv3 but no itv1, or itv2 ( which is strange considering I can get Itv2+1) , No channel4 ,E4 ,More4 or film4, NO channel5 but I can get 5* & 5usa Ive got the stupid qvc type channels and a couple of other channels. also I only have 2 radio channels.The channels I do receive all have a excellent picture & sound and I receive channels 1 to 5 through the ogue ariel at the moment tried rescanning with no luck any suggestions?