Fitbit Product Experts Alumni are retired members of the Fitbit Product Expert Program. Learn more
If you've changed phone and still have the old phone around then make sure it doesn't still have a bluetooth connection to the fitbit that may be blocking connection to your new phone.
Also, have you checked that your new phone is supported by fitbit at www.fitbit.com/devices ?
Fitbit Product Experts Alumni are retired members of the Fitbit Product Expert Program. Learn more
Did you get this working in the end?