Sorry, it's hard to make sense of your post.
- How long have you been with Public Mobile?
On the legacy rewards you will get $1/ plan cycle per calendar year you have been a customer, up to $5. *
If you are just running the plan continuously (instead of suspending it for 85 days, activating it for a cycle, suspending it for another 85 days... saves money, but you won't be able to use the phone in any shape or form while it's in suspension), leave "subscription" / autopay on, this will give you another $2 off per cycle.
So, essentially without doing anything, you are getting (up to) $7 off, making the $15 plan a $8 plan.
Are you sure you didn't lose some referrals, your numbers indicate that you might have had 5 referrals on the $25 plan, and then 4 on the $15 plan... As I say, I find it hard to understand.
When you say you had to pay for the switch - if you changed plans effective immediatly mid cycle, yes, it will charge you the full new amount of the new plan (rewards will be credited within 72hours of the payment). Better choice would have been changing plans at renewal, so that your rewards are applied normally.
In my opinion, 12 x $4 = $48 / year is a reasonable amount to hold onto a number and account.
As mentioned above, you could also suspend the account to save more money, but you want to stay on top of those dates since the account and number will be permanently lost if you miss the suspension window of 90 days.
Other cheap-ish option would be porting to SpeakOut ($25/year, physical SIM, works in Canada only) or a VoIP service like Fongo or voip.ms. Porting to / from the later can be tricky/time-intensive/need-a-one-time-fee.
* Suspension of more than 60 days will delay your rewards accordingly. Say you signed up on January 1, 2020, your plan has been continuously active, so your first rewards, 1$ will be taken off your bill on your renewal on January 25/2021. You then suspend your plan from July 21/2021 until October 16/2021 (85days), so your loyalty rewards will only move up to $2 on the renewal after March 27/2022, and so on.
