Change mobile number listed on my account

Hi I need to change my mobile number as the last digit is incorrect. I’m not sure why as autofill is correct and I wouldn’t have put the digit it has at the end regardless. 
I also only got my broadband installed on Thursday and I’m already having an engineer out to sort it out as the broadband does not work even going through the online checks. I need your mobile number updated before the engineer comes on Wednesday.