Hello. I'll be glad to help you with this issue. Just a moment please.
Manual for Panasonic KXTGEA20 Handset:
Page 40 in the second document mentions Erasing Messages. Please see screen print attached below.
According to the document, to erase all messages Press ERASE 2 times while the unit is not in use.
Where you able to erase all the messages?
Is Your handset paired to a Base Unit?
The messages are cleared from the Base Unit. I provided the steps for the KX-TE210. If you have a different Base Unit please supply the model#.