Answering machine will not pick up (li...

Our Uniden brand phone currently broke (microphone) so we purchased a new Panasonic phone. We have earthlink VOIP phone service. The new Panasonic phone (think it was this one KX-TG6433M) WILL NOT answer any incoming phone calls?! We returned it thinking it was broken and purchased a different Panasonic phone system (KX-TG1033S). Same exact problem. Answering machine is turned on, 5 rings, earthlink voicemail is turned on, 8 rings. I contacted earthlink and they said to turn off the voicemail (which I've tried before) and that doesn't make any difference at all, now it just rings say 10 times, and says we are unavailable try again later, nice. I would think this is a well known problem someone would have an answer for that offers this service??? The thing that is completely odd is I can just plug in the old uniden phone system, and it will answer fine with no problems. I don't get it?