No need to visit Apple. The phones from Virgin are unlocked according to Scott's post so no need to unlock it and if it was "Locked" you would need to visit a Virgin Store.
I think the issue with no service is because you are on a plan with Woolworths and they will not release your number until the plan is cancelled.
I suggest you ring their Customer Care line on 1300 10 1234 option 5 (normal charges apply) between
8am to 8pm Monday-Friday (AEST/AEDT),
9am to 5pm Saturday
10am to 5pm Sunday
9am to 5pm (AEST/AEDT) National Public Holidays
and then ask them to cancel the porting of the number and check if you need to get a new SIM from Woolworths and re-activate the number with them. Use the SIM from the OPPO if they tell you it is still ok to use (don't use the OPPO just use it's SIM), or if you had to get a new Woolworths SIM use that new one, in your iPhone. Don't use the current ALDI one.
That should let you get back to phoning for the moment. Back up all the data from your iPhone to the iCloud. Next, buy yourself a new SIM from whomever you want to use eg ALDI and register and activate it on the OPPO but DO NOT ask to transfer your old number, it will give you a new number. Then let all your contacts know your new number. Once you have informed everyone of your new number, take the new SIM out of the OPPO and put it in your iPhone. Finally recover your iPhone data backup from the iCloud.