Echo over Phone

MODEM:- NF4V

PLAN:- Fibre

Been struggling with echo over my phone. Doesn't happen all the time. Just tried to call Eset and they were experiencing echo at their end. But as soon as I called slingshot, no problemmmm...typical.

Today I called slingshot, and had to make sure that Enable Echo Cancellation was ticked under Voice modem settings. It wasn't we ticked it. I thought all was well.

That's when I called Eset. They are getting the echo at their end. Its either me or the person on the other line.

Anyway how can I get this issue resolved? Have new modem/phone (standard phone no power cord needed). Been struggling with this issue for months now.

Thanks in advance.