The above may occur for the following reasons:
Your ad is the only one with this keyword. In this case, the 1st position placement and the guaranteed placement price may be the same as the minimum CPC. The premium placement price may be higher.
All advertisers whose ads were selected for impression in the guaranteed placement block based on the keyword you selected use the lowest position in block.
You might get clicks for the “old” price if you changed the bid in a paused campaign, and then restarted it. It takes about 30 minutes to activate new bids. During this time, clicks are charged at the previous rate that was set before the campaign was stopped.