OK I have found out the reason why! It's quiet laughable. My visa was due to run out on the 17 April right. So my new visa was 17 April to 17 May. The free visa was for 30 April. So they decided to charge me for 1st May to 17th May as they didn't know the amnesty would be extended. if I had not gone there I would have been OK. It's quiet funny na. 555!!
I would like to point out the main reason for this question was to confirm that I am definitely covered by this free extension. You can understand my confusion when payed for visa on April 17 and told to come back this month. Only to be told it's free! Two different immigration officers which one is right?