I am trying to land an A321 but whenever I get close to touching down the autothrottle comes back on and I can't shut it off.
Show the overhead panel ( Shift 5 ), and you will see three flight control buttons in the mid left region. Click those three FLT CTL buttons to OFF , and you should find the A321 behaves normally.
Also, on final before flare and touchdown, you should turn Auto throttle of first, then turn the Auto Pilot off , in that order.
Remember to use reverse thrust whilst braking on the tarmac - which on my setup is the [fn] key and the [F2] key - - then [fn][F1] to stop the reverse thrust.