This solution may help fix the problem especially when you already tried replacing the keypad flex matrix but still the keypad doesn't work.
The following solution shows the entire connection line paths of the keypad filter IC from the keypad flex pin connector for easy check up and troubleshooting procedures.
Nokia E72 Keypad Not Working Problem solution with keypad filter IC jumper ways
The solution above shows the keypad connection line paths within the two keypad filter IC deeper keypad problem troubleshooting on Nokia E72.
The two keypad filter IC is mounted just near the keypad pin connector, you may need to replace these filter chips if the keypad doesn't work, especially when the device suffered wet or water damage.