If you log into your BT account, and try add BT sport as an item does it let you select it to add to the account? It should say free next to it.. It should give options about where you want to watch it? If it wasnt pre-selected when purchasing the sim..
@XxSteveDxX if you need any help getting your BT Sport app activated send over your details on the 'click here to contact the mods' link in my forum profile. You can find the link by clicking on my username.