Default [Q] voicemail and sd card problems

OK,2 things wrong here.I bought a sealed in box s4 from eBay which was supposed to be unlocked.I found out it was locked o2.I flashed stock Samsung 4.4.2 Android then successfully unlocked with
o2 unlock code.I can't change the voicemail number from o2 number to my giffgaff voicemail.I also have I installed navigon satnav app but when I try to download maps it say my device has no SD card but it does.and its recognised by my files app.Any ideas?