I never even thought about the payback! Why would that be lost if the account is still active? Not too bothered about the £5.53 credit but the payback is totally different!
The giffgaff's Terms and Conditions that relate to payback points state: (my bold)
7.5 To qualify for Payback Points you must:
(a) be aged 16 years or over;
(b) have an active SIM Card at the Payback Date; and
(c )have successfully made a connecting call or SMS to any mobile or used mobile internet at least once in the 3 months prior to end of the relevant Payback Period.”
7.6. If you select a PayPal transfer, you are responsible for providing us with valid PayPal account details. If there is a refund generated from the member-side back to giffgaff the full amount will not be rolled over or paid to a different PayPal address.
7.7. We may suspend or discontinue the Payback Points scheme at any time. In this event we will provide notice on giffgaff.com.You would stop accruing Payback Points but if you are eligible for a payback before the suspension or discontinuation of the Payback Points scheme, we will honour it.
7.8. If your Account becomes inactive (through closure or porting of your mobile telephone number) your Payback Points will be removed.
I cannot find anything that says that points removed under clause 7.8 will be reinstated if you activate a new SIM on the account.
@t_will may be better placed to explain what happens with payback in situations like this.