I changed my plan but the bill remains the same

Hi, 

Could someone explain to me how this works? My next billing circle is 27th July - 26th August. I changed to a less expensive plan recently but the bill remains unchanged. Does that mean I need to pay the same money for the next billing circle while using a less expensive service? Or will I get refunded? I was trying to talk to a representative but can never connect to one...

Thanks