Your tier was extended for three months on 29 Dec, because you had not already requalified by that date (or possibly by the day before for calculation purposes)

You now need to accrue 540 qpoints in the 12 months between 1 April 2023 and 31 March 2024, or 1,080 qpoints in the 24 months between 1 April 2022 and 31 March 2024. If you achieve either of those your tier will be extended on 1 April until 31 March 2025. Tiers are only renewed on the current expiry date, not when you reach the threshold.