You need to change it yourself on your account for them to update it x
Mine just stopped, although I did get one more than I was expecting.
Your earnings are reported to them monthly by hmrc so payments are always determined by your earnings. Your assessment period will also have an impact for example if your assessment period is from the 1st to the 29th of a month and you went back to work on the 30th you'll be classified as having zero earnings between the 1st and 29th but your wage will be used for the following months payment calculation
Any type of change of circumstances always update them it will prevent you being over paid x