Are you sure you have the right activation dates ? activation dates only happen weekdays, check your order confirmation email to verify.
Is this a new line and broadband, a ( BT type line) working phone line existed and you just are adding broadband to it, or a change of broadband supplier ?
Do you have a dialtone, if so , if you dial 17070 is the correct number announced ?
If the phoneline isn't working it's unlikely that the broadband will work, and if work is required to get the line to work, then the date for broadband activation may slip as the need for work on the line may not have been realised until the activation date, in fact they may still not know its not working and it may need you to call and report the line not working.
If the phone line works with the correct number it may be that although the date for connection has passed , the work to connect the line to broadband hasn't been done yet, in which case it may be done soon.
Without knowing what you had previously it's hard to know where the problem may be, for example I know of an occasion where someone moved from Virgin Media to an Openreach based provider but plugged the new router into the VM master socket rather than the Openreach master socket, and wondered why the new service didn't work, as they didn't realise they were totally separate networks