A deposit limit works only if you set it before the session starts. If you set a weekly cap of A$300 and hit it on Tuesday, you can't top up again until the period resets on its own, whatever the reels are doing. That is the point.
Size the cap to how you actually play. A high-volatility pokie at the A$8 max bet allowed while a bonus is active turns A$300 into 37 spins, and a dry run of 37 spins is a normal outcome on that kind of maths. Thirty-seven spins, not a session. A loss limit or session timer on top of the deposit cap tells you when to stop, even if the balance still has money in it.
Bonus buys and fast spin modes speed up the losses. A buy usually costs 50 to 100 times the base bet, so at A$1 a spin three buys at 100x use up the whole A$300 week. At most offshore operators, some limits are changed in the account and others only through support. At Tower Online Casino, the exact options for your account are listed in the Responsible Gaming section, and support can apply them too.