We have noticed that the March 2020 payment was deducted at S$30 instead of S$21

A pleasant day to you, @vma.

My colleagues already provided a great response to the question that you've posted. You can refer to these links to see what they suggested doing in this situation: 

• Notice the payment of S$30 deduction for march 2020 instead of S$21?
• Why monthly payment deduction at S$30 instead of S$21 for march 2020?

I've also added here a link that you can check out about the plans and prices of QBO for reference: QuickBooks Online Plans.

Please know that my doors are always open to help you if there's anything else you need. Take care!