Hey there @Soni8195,
Welcome to our Community
It is possible to take a payment arrangement with our Credit Operations department if ever you wish to pay the invoice after its due date, you would simply need to contact them here or by calling *732 from your Fido phone. Keep in mind that late fees will apply for any payments received after the due date.
As for the plan, you can certainly change it. To avoid having to pay the remaining the subsidy on your device, you would need to select a plan from the same category as yours.
If you'd like to go ahead with the plan change you can reach out through here or we can send you a PM on the Community, let us know!