Could Somebody Well-Versed in Cashrewards and Amaysim please help me?

Due to a monumental screw up I've managed to lose my nice phone number through Aldi. I like the Amaysim number selecting system so I need to get the cheapest SIM possible to select a number I like and port out to another company. I've been through this in the past but only following guides of what I see posted on here so I'm not trusting myself to get this right. Cashrewards and Amaysim Plans

Amaysim are running an offer on the 2GB Unlimited plan for $15 instead of the usual $25 whilst CR offers $20 but there is no mention of the coupon on Amaysim's site on CR. So to me this says if I pay $25 through CR the SIM will cost $5 after cashback but if I dare use the coupon offered on Amaysim the CR won't count and it'll cost $15 instead of +$5 profit, correct?

Another thing I've noticed whilst browsing (though no use to me in this case) is the 2GB data only plan available on Amaysim for $15 without a coupon whilst CR is offering $20 cashback, this seems too good to be true and not have been posted here. Is there profit to be had?

Alternatively if I select PAYG and then add the optional 2GB data plan for $15 (get the PAYG SIM for free) would that nullify CR? Or I suppose it would give the $3.50 cashback for activating PAYG.

I'm rambling. Is the best option the $25 2GB Unlimited with with $20 cashback?

Of course, if there's another company or better way to search a custom number without paying a high premium for it I'm all ears.

Thanks.