If I turn off my Wi-Fi can they track my IP address?

If I turn off the hub would this stop them tracking me. They also say they can track my phone using the IP is this true? And how can I stop it? Should I take out the SIM (it's an iPhone btw)

Yep.
Stop it by destroying the phone.

It makes no difference if things are later turned off, it's all in the connection logs.

ISPs are required to keep records of connection data, which is available to the police when required.

Simply don't do anything illegal.

They would know your address anyway, as it is where your router is installed to provide you service!
Not only could they track your phone, they can follow your directions, as when you travel your signal is pinged off other transmitters as you move, anywhere.

Who are they? No outsider can track you from your IP address certainly not with any degree of accuracy. You private address is known only by your ISP and they would only divulge this to the authorities with a Court Order.