Check out your usage - https://selfserve.publicmobile.ca/Overview/viewUsageChangePlan/ - from there, take note of how much data you use per month. If you're not using all the data you're paying for, the easiest and fastest way to reduce your bill is to switch to a plan with less data. You could save $10 a month by going one tier down.
Autopay is also an easy way to save $2 per month. And for every friend you refer, you save $1 per month. Get a few friends switched over and the savings add up more - as far as I know, there isn't a limit to how much you can save through referring friends.
Tax is inevitable, so there's no way to get rid of that. But there are other, more esoteric ways to make sure you're not spending more than you should. Chiefly: if you're able to, pay your credit card bill off at the end of every month. If you don't, you're effectively being charged nearly 20% extra for every bill cycle....that's a really big one.
How else can you lower your plan amount ?
You can refer a friend, the amount changes, I think it is one dollar per referral, plus if a promotion comes up you get an extra 10 dollar bonus. You can help in the community by answering questions, or asking questions, and even bravo on comments, already made. Then you get a dollar for each year you with PM. Plus the two dollar auto pay. Some people have got their bill at zero, but this is on going, you have to work it every month. And watch the community board, sometimes you can get etra bonus for some new promotions, once in awhile contests?