Issue with Standard SMS feature

We have enabled the High volume SMS feature for sandbox and production numbers .as the result standard SMS feature was not working anymore for messages, so we need to switch back to low volume SMS feature, we rise a ticket about this issue on this portal"https://developers.ringcentral.com/support/create-case", and now the case was closed, standard SMS feature is now working only for sandbox account in production has still issue

it shows errors like this

{

"errorCode" : "FeatureNotAvailable",

"message" : "Phone number doesn't belong to extension",

"errors" : [ {

"errorCode" : "MSG-304",

"message" : "Phone number doesn't belong to extension"

}

in production, is number switchback not working or any other issues