Imobaliser alarm keeps going off when I put ignition on

try locking and unlocking the driver door with the key

The clue is the remote control low battery (or replaced) == it's lost it's 'code' and needs to be 'reprogrammed'. Until then, the imobaliser (in the ECU computer) will lock the ignition. As soon as you tried to start the car the alarm was triggered (with the ECU locked the engine turns over but won't start).
Take it away from the cowboys and to a garage that knows want they are doing = and don't listen to the idiots who failed to actually read your question and would have you start taking the car apart or replace the starter motor

the car is imobalised, try disconectint the earth from battery for 5 mins and reconect, car should start

try locking and unlocking drivers door lock with the key

Call the Dealer you purchased the car from, and have them walk you through it. Act as if you are stuck in the middle of nowhere.

your car alarm battery key set is going dead.

If you lock your doors with your remote or the power locks you need to unlock them with the remote or the alarm will go off. to reset the alarm you need to put the key in the ignition and turn it on and off 3 times fast.

Disconnect the battrey wait 30seconds reconect put your key in and turn ONE click "i" possition and press your fob button (same alarm system as my carina e Solair, and this happens for me once a year first time cost £165 so i learned how to do it myself)

have you tried replacing the cdi unit this controlles the spark to the coil ??? get back to me

maybe a neutral safty switch