Landline can not dial out. There is a dial tone and I can receive calls

I have two land lines with the same issue:   I can not dial out.  When dialing, I hear the dial tone, the phone dials the numbers, then I get the dial tone back again.

I can receive calls.

This started this evening after I called a customer support person about a different issue.

I suspect that it is a configuration problem with my account.

I have tried to get help through chat but have connected with 4 different agents who have all reset my modem which disconnects the chat and then they never reconnect.  Very frustrating!!

3 hours of chatting and no resolution.

How can I fix this problem with the landline?