Here's what I'd recommend @tillyp
Go to a local place that sells Public Mobile payment vouchers.
Once you have one, dial 611 from your PM phone and follow the prompts to add that payment voucher to the account to reinstate your service. For this payment option, you will not need the PIN to apply the voucher (you would need the PIN to apply a payment using a registered payment card)
After that's been done, follow @hairbag1 information on how to reach a customer support agent to get the account access and payment card details updated and confirmed.
