We have had to do this a few times, not totally sure this will work for you since I'm not sure if you are in the US or not but if you are could give this a try:
https://reportarobocall.com/trf/# - For Enterprises - are you concerned that your calls are being labeled as nuisance or fraudulent calls or that your calls are being inadvertently blocked? This website will help TNS Call Guardian validate the characterization of your business telephone numbers and protect against erroneous blocking of wanted calls.
And this
https://www.freecallerregistry.com/fcr/# and this https://firstorion.com/register-your-number/
These are all free and basically you are registering your # with them so you don't get marked as spam. If that doesn't work you have to find out what carrier is marking you as such and contact them directly (just call their support and stumble through it)
Somehow this worked for us and after 1 week our numbers were no longer marked as spam or auto blocked by carriers.
Hope this helps!!
