Would you be able to check your IP to make sure it's showing up as a Singapore IP? You can do that here. If you set up your account outside of Spotify then you made need to change it there instead. If that doesn't apply then I'd suggest reaching out to Spotify Cares through this contact form, their facebook or twitter, they should be able to get you sorted with this.
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I just moved from Singapore (family membership cost of 15SGD) to the UK (same membership now nearly doubled to £15)... Can't complain, was getting it for a cheap rate in Singapore, but good luck, it's much cheaper there.