I finished paying my phone contract off in August  and it just charged me my normal amount for the next month (Aug-Sep) so still paid the full amount for phone and sim, even though the phone side was paid off. I’m wanting to switch it to a lower deal now the phone is paid off and just pay for the sim contract but when I go to choose it as an option it’s saying my next payment will be taken out in October. 
My normal bill comes out 17th so why isn’t it starting the first payment of the new contract this month instead of next. 
Does that mean I’m going to be paying the current contract amount again this month?