Hello Mahon,
Firstly, if you were not aware, you should note that this forum is community-driven and not intended as a venue for customer services. We do not have access to customers' accounts and would not know the specific details of your situation.
You should note that it's possible your current plan is not compatible with financing a device (ie BYOP plan) or is no longer sufficient for financing a device. If that is the case, you would need to switch to a current suitable device financing plan in order to finance that device (see here).
That said, as to your question, you can change a plan to one within the same category with the Fido Payment Program (see here). However, if you change your plan to a different category during a contract, you will likely be charged the outstanding balance for the device.
If you wished to discuss your situation, you would need to contact customer service. In addition, they can also be contacted via Live Chat, Facebook, or Twitter. Those methods can be accessed via the contact page posted above.
Hope this helps 😀
Cheers
