Can't setup Charge 2 on iOS shows error 500

[FBHELL]

I purchased Fitbits to use as tracking devices - we set them up under our names as the device cannot be used by Children, unless Parents don't have a device. A family account can't be set up as we purchased the Charge2, not the ACE.

In any event, I am trying to set up an account for my son - DONE, but the device refuses to be accepted by his account, which is on an IOS device. I have deleted my account and waited 60 hours to add the device to my Son's account and it reaches a point where it asks for a 4 digit pin to be added to the APP.

Once we add the number, onto the IOS device it goes in circles and gives an Error500.

Fitbit Support is useless and I am at wits end having wasted money buying a device where customer service and ease of use are definitely not on offer. 

I have deleted the app and tried to shut the Fitbit Charge2 down, but without success. Any help would be much appreciated!

Moderator edit: updated subject for clarity

[AlvaroFitbit]

@FBHELL It's great to see that you've visited the Fitbit Community! Sorry to hear that you can't setup your Charge 2. As far as I know this happens when you deleted an account where the device was paired to. Try the following:

1. Log in onto the old account.
2. Agree to recover the Fitbit account.
3. Go to the account,
4. Tap on your tracker.
5. Scroll all the way down.
6. Tap on remove your tracker from your Fitbit account.
7. Log out from the account.
8. Log in to the new account.
9. Set up the tracker on that account.
10. Log out to the account.
11. Log in back to your old account.
12. Delete your old account.

Let me know how it goes!