Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, bear with us; re-confirm and post back with the complete model number of the base unit.
Appreciate the additional information.
Please click HERE.
Have you tried the above steps ?
After the above procedures, have you then pressed on SAVE and then OFF on the handsets?
Did the message "Base in registering" displayed on the handsets?