Then how come we receive circular that there will not be any increase in the premium? 

The Star - Insurance Premium Unchange

If by Jul and your birthday is up, then it make sense that it goes up.

Also take note that the premium can be adjusted with minimum slack or more slack depending on your budget. More slack means more money is invested to built up the cash values to have the policy with better sustainability 
For age 51 next birthday, male nonsmoker

1m death or tpd
2m if death due to accident
3m if death on public transport
4m if death whilst overseas

Premium target sustainability till age 80, Rm1165 mth
Premium target sustainability till age 90, Rm1651 mth

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For the medical with Rm500 Room, Rm1.98m per year, no lifetime limit, Rm300 deductible
Sustainability age 90, Rm956 mth
Sustainability age 100, Rm1167 mth