Try without quotes

src/freedombone-addsipuser

@@ -77,7 +77,7 @@ function update_sip_user {
                 USER_FOUND=
             fi              
         fi
-        echo "$line" >> $NEW_CONFIG_FILE
+        echo $line >> $NEW_CONFIG_FILE
     done
     mv $NEW_CONFIG_FILE $CONFIG_FILE
 }
@@ -97,7 +97,7 @@ function add_sip_user {
             echo "<display>$MY_USERNAME $EXTENSION</display>" >> $NEW_CONFIG_FILE
             echo '</user>' >> $NEW_CONFIG_FILE
         fi
-        echo "$line" >> $NEW_CONFIG_FILE
+        echo $line >> $NEW_CONFIG_FILE
     done
     mv $NEW_CONFIG_FILE $CONFIG_FILE
     usermod -aG sipwitch $MY_USERNAME

src/freedombone-rmsipuser

@@ -65,7 +65,7 @@ function remove_sip_user {
             fi
         fi
         if [ ! $USER_FOUND ]; then
-            echo "$line" >> $NEW_CONFIG_FILE
+            echo $line >> $NEW_CONFIG_FILE
         else
             if [[ "$line" == '</user>' ]]; then
                 USER_FOUND=