hi.. need advice and anything

i purchase a house with the value lower than the market value (by comparing to the next phase launching value)
new lauching is around 320k while i'm getting it at 250k (first launch was only 270k)

the reason given by the owner need fast cash to settle everything..
the owner still owe the bank around 230k only..

everything goes right... until today.. a state government valuer call me asking why the value of the house is so low.. and require me to top up more on stamp duties..

1. do i have to pay more stamp duty just to level with current market value?
2. is it somthing wrong here on the purchase.. until now.. i don' feel nothing fishy yet..

i already withdraw my EPF and already paying 8% downpayment to my lawyer..
thanks..