Hi A_D, thanks for your reply which is clear. I just had a call with DIPB. The person who answered the call confirmed 3 points (i) Vocational english evidence and above has 3 years validity as per DIPB website, (ii) Vocational english could be substituted for Functional english, (iii) the case officer may not differentiate Functional vs Vocational or upper level in their decision making. However, as she is not the decision maker, she can only provide reference id# of the call and suggest me to quote this ref in an explanation letter then upload the letter along with a new scan of the same IELTS score, for the case officer to reconsider.
I did as per her advice. In the same time, my spouse also booked a test but sadly the earliest date we have where we live is 30 June which means we expect a few months of delay.
I will update you guys if I have a positive response, thanks