Assuming the above function is called from an event somewhere, you could attempt to set an event break point at the entry point to this and step thru to gain some understanding. First thought if the request is being triggered by a submit input within a form it may be triggering the default form action instead of the intended code. ( ie https://developer.mozilla.org/en-US/docs/Web/API/Event/preventDefault)
Outside of plans, there is also great value with Boost 12-month prepaid if you can plan for a big one-off payment per year. I originally chose it due to having better coverage than other providers (uses the full Telstra network) and low per month cost for primarily call/sms usage.
I’m currently on a $230 recharge for 12mo/160Gb, making this $19.20/month or $1.44/Gb. Due to change in avail plans, next recharge will be $300 for 12mo/240Gb (calculates to $25p/mo $1.25/Gb)