Odd way that Maybank Platinum Visa calculates the min. spend?

I received only $30 cashback (and not the expected $100) for the most recent quarter, even though my credit card statement for each of the past 3 months has exceeded the $1,000 threshold.

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FYI my credit card statement is dated 23rd - I recall checking whether the credit card statement date could be changed a few years back but was told it was not possible.

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Called the customer service hotline and was told that the min spending criteria is calculated based on 1st to 30th/31st each month, which was why I did not hit the min spend for September.

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Seems really odd - can anyone confirm this? It does not make sense for them to base the min spending criteria on partial periods that are not yet "billed" in the credit card statement.