My message light on the handset keeps flashing and I have deleted all messages and tried to reset it by taking the phone off the reciever and holding down the find button for 10 seconds, this causes the flashing light to stop for a few minutes but then it begins flashing again.

You have unheard messages on the voicemail system provided by your telephone company. This system records messages when someone calls while you're already on the phone. Please contact your telephone company for instructions on accessing their voicemail system.

I had the same issue on my RCA 25255re2 and worked with customer service at RCA. They had me hold down the delete button for 5 seconds, release the delete button, then press delete one more time. That cleared the phantom L1 message waiting issue we were having at my office

Hi,
In the message settings msg center number may be changed. Please check with your service provider and input the correct msg center number.

You have unheard messages on the voicemail system provided by your telephone company. This system takes messages when someone calls while you're already on the phone. Please contact your telephone company for instructions on accessing their voicemail system.

That is the message waiting indicator, it is telling you that your Call Notes (Or whatever your service provider calls it's voicemail) has a message waiting. If you do not have a message waiting, you can turn the light of by following these steps:

Resetting the voice message waiting indicator
When you receive a new voice mail message, the new message LED on the top of the handset flashes and
appears in the handset display. In the event your message waiting light gets out of sync with your phone company’s
voice messaging system, you can manually reset it back to the “No messages waiting” state.
Press and hold FIND on the base for five seconds.
Note: The handsets connected to the base will start to beep, however, keep pressing for five seconds.
A beep sounds and the message alert tone is reset.

Try this steps to perform soft reset

1)Press and hold down the ALT key on the smartphone.

2) While holding down the ALT key, press and hold down the right-hand CAP key.

3) With both of those buttons still pressed, press the DELETE key. The display on the BlackBerry smartphone will turn off to indicate that the reset has started, and the keys can now be released

Still if you face same issue Download and install the latest BlackBerry Device Software, which is available from the BlackBerry.com

Hope this is helpfull for you

reset your base unit by disconnecting power, then hold find hs button while reconnecting power.

Press down the "find handset" button until the paging beep stops (about 5 seconds) and this will reset the indicator lights on the handsets.

To reset the indicator(Red light flashing on handset), press and hold the find handset key for 5 seconds or until the light flashing stops(10 sec).

Resetting the New Message LED
If the LED remains on after you’ve retrieved your messages, you may need to reset
the indicators. With the phone is in standby mode, press and hold find handset on
the base until the paging sound stops (about 5 seconds).