Plan changes on an expired/suspended account can only be done by a moderator.
Click this Moderator_Team link to send a private message for assistance. Include your account # or phone number and the details of the plan you want.
More info on moderators: http://productioncommunity.publicmobile.ca/t5/Knowledge-Base/Updated-Contacting-our-Community-Modera...
However:
Are you really sure you want to change plans? If your plan was from prior to July 13, 2017, and I'm pretty sure it is, since it hasn't been 90 days from that date, you have a grandfathered plan that is great value at 2 GB of LTE data per month for $40/month. You're exchanging that for a plan that costs $57/month for 2GB of 3G speed data (which is capped at 2.5 mbps) and the only advantage is Canada-wide calling. If you really need Canada-wide calling, I would advise buying PM's 400 minute long distance add-on for $15, which will roll over forever until used up. You could buy that every month on top of your province-wide plan and it would still be cheaper than the new 30-day plan for $57, unless you are going to use well over 400 mins of nationwide calling per month. With PM's new pricing structure, LTE data plans are way more expensive than they used to be before July 13. Once you change plans, you can't get the grandfathered LTE plan back.
