I cant hard reset my phone

Hello Festus,

you have 2 choice:

1) enter in the recovery partition and format the phone doing this:

shut down the phone, the push and hold volume down + power + home

till you will see something different from what you are used to. Something like an 80's computer interface.

Than choose WIPE DATA / FACTORY RESET

take a look at this video: https://www.youtube.com/watch?v=EIGst3ed...

2) When you will have reset you phone, if you still have demo limitation, you have to use a tool called ODIN and flash (install) and original firmware (called stock).

You have to search on forum like XDA, because is the only way for give the phone a full functionality.