<p>The BT Sport app closed on 12th October and has been replaced by discovery+. <a href="https://community.bt.com/t5/TNT-Sports-on-TV-Online-player/The-BT-Sport-app-is-closing-on-12th-October/td-p/2312034">Find out more about activating TNT Sports on the discovery+ app</a>.
They are not transferable, you would need to give 30 days notice to end the BT account, then contact Sky. Be advised that if you're within a minimum term with BT you would face early termination fees, Sky would most likely ask for a new minimum term.
If it's simply down to costs, ring the Loyalty team on 0800 800 150 and see what discounts are available.