Wrong contact synchronisation with 2 iPhones
You can try to see if your phone had saved a backup to your computer upon last sync. This would mean restoring the phone from backup, which isn't always ideal depending on the situation.

Unfortunately, it's not easy because iCloud was likely left enabled on the old phone, which synced them up to the cloud, and then down to your phone.

Else, here is a suggestion provided from the Apple discussion forums:

(BEFORE YOU BEGIN, MAKE SURE YOUR ICLOUD ACCOUNT IS SIGNED OUT OF THE OTHER PHONE!!!!)


Ensure the device is connected to your local network.
Start the restore from iCloud back up.
Allow the devices settings to restore (watch for the confirmation of completion).
As the apps begin to restore pull the connection to your router WAN port (the one that goes to the telephone point/cable modem).
Wait for the time out confirmation.
Navigate to settings > iCloud and turn off contact syncing (keep contacts when prompted).
Reconnect the router to the internet and let the restore process complete.
Delete any iCloud contacts from iCloud.com on a computer.
Navigate to settings > iCloud and turn on contact syncing (merge contacts when prompted).