Messages not being read

Hi, I have sent 5 messages today to 5 people interested in my property listing. The messages are showing as delivered but not read!
Seems strange that I haven’t received a single reply to any of the messages. Has anyone got any ideas of how to check if there is a problem?

Have they left a phone number too? I sometimes get these with enquiries.

Thankyou!! I hadnt realized we had access to alternative contact details!
I managed to find their phone numbers, which was really useful.