Pay as you go gold rewards

Hi, I am using T-mobile with my unlocked iPhone from abroad.

I used $50 prepaid plan which provides me unlimited talk, text, and data. However, as I am not a heavy user of the mobile phone, I changed my plan to PAYG after a month of use.

I refilled my account with $100 yesterday and changed the plan online.

Now I check my status in the morning and found out that I have 666 minute talk.

I am wondering how I have that amount of talk? My account status says that my account balance is still $100.

As far as I know, PAYG plan offers me 30 minutes for $10, 160min for $30, 400min for $50, and 1000min for $100.

I wanted to pay $100 to earn gold rewards status to keep my 1000 minutes of talk for a year.

Please help me out.

Thank you.