Can't use text messages to respond to guest inquiry

[Libby26]

Hi 

does anyone out there know the answer to this one? I am a (relatively) new host and previously hosted in other countries. I can receive messages in text form on my phone, however when I try to reply a get a message saying 'unfortunately we could not process your response because your number is registered to too many accounts'. 

I no longer have any other accounts, so cannot figure out how to fix it. Any ideas welcome!

Thank you all....