SAPO says the deadline for post box renewal is 31 December 2018.

If you have not received your invoice, please request a re-issue of your invoice by phoning us on 13 POST (13 7678).

While I believe that you can renew your PO Box lease for more than one year, you can't renew it for less than one year.

When you’re in branch ask for the Digital Check & Send service. Left arrow to indicate to go back Back to Delayed, lost or damaged items. THE South African Post office (SAPO) is reminding it’s customers to renew their postbox subscriptions.
Closed boxes may be made available for new customers.
If your payment is more than 10 days late, you need to go to the Post Office where your PO Box is located to pay your renewal fee and a handling fee to cover our processing costs. Manage your mail. Compensation for lost or damaged items. We’ll help you to get it right first time for just £16.00, bringing the full fee to renew your passport to £91.50. Left arrow to indicate to go back Back to Delayed, lost or damaged items. The Post Office’s general operations manager Sbu Xaba said,”Post boxes are readily available and safe and they give customers access their mail at their convenience.” Left arrow to indicate to go back Back to Receiving. Compensation for lost or damaged items. Commercial customers may pay by Account to renew their Postal Box rentals. After 10 days of nonpayment, your mail is treated as undeliverable mail and your PO Box is closed. Bring your old passport into one of our selected branches and we’ll do the rest for just £16.00. If you think that you won't need the box for the full year, you will still need to pay the full year's renewal, and then when you no longer need it, you can cancel the service and get a refund of the unused whole months left on your lease minus the cancellation fee. We’ll sort everything out and give you a receipt for your payment. It costs £75.50 to renew or replace your passport if you apply online or £85 if you fill out a paper form. How to renew your adult passport. You can pay with cash or debit card at the Post Office and we don’t charge for electronic payments (though some banks may charge – check with your bank if you’re not sure). Manage your mail Arrow to indicate more links. Contact your Canada Post representative or the Commercial Service Network at 1-866-757-5480.

PO Box renewal payments are due on 31st March. You will not be able to pay online or at a self-service kiosk. Paying a bill at your local Post Office is easy – just bring what you need and tell us how much you would like to pay.

Find your nearest branch. Contact your Canada Post representative or the Commercial Service Network at 1-866-757-5480.