POTSModem query

[Symptom]
Hi I am experiencing a very strange problem when sending the msi query
select * from Win32_POTSModem. I rely on the result from this query to detect
some up&running modem names with a condition where ConfigManagerErrorCode >=
0 AND DeviceType = 'External Modem'

It has been working for a long time. But now the query "select * from
Win32_POTSModem" returns nothing or probably an empty string.

[Things could possibaly went wrong]
I have been testing 3G devices for a while and I have installed/uninstalled
different 3G devices from different manufactures more than 100 times on my
computer.

[Solutions I have tried]
1.
net stop winmgmt.
delete the %windir&\system32\wbem\repository directory.
net start winmgmt

2.
"winmgmt /clearadap" to clear prior WMI and register it again

None of them helps me to get back to normal. Does anyone have any idea
about this issue? Thanks in advance.
BR,

Pan

--
Toe the line
Thread the needle
Think outside of the box