Why can't I verify my domain on CM Commerce for email newsletters?

[oldlutheran]

We have lost our ability to send out email newsletters using the App CM Commerce. We have been using them for several years and suddenly we are receiving the message that our domain is not verified. We have reached out to customer support several times and all we hear back are generic comments with links to their documentation about verifying the domain. Our DNS settings are correct according to their documents but we have not been successful at getting our domain verified. What are other reliable apps that you recommend for customer retention and newsletters? My last request for information took 96 hours to receive a reply.