If I was overcharged for this months bill which I already paid, will I receive the $20 I overpaid on next months bill which will be available on October 7? I opened my TMobile account with a single line on July 6. My monthly plan rate was 75 for the line, plus 7 for device protection, 9 for the device payment and 10 for the One plus which equals 101. I opened a second line on august 31 during my bill cycle. When I received my bill on Sept 7, I was still being charged $75 for each line instead of the 65 for each. I called customer care and they said I would receive the credit for the $20 I overpaid on my next bill? I just want to make sure that's how it works.