Since a month or 2 my Philips VOIP8551B/36 Skype Phone no longer connects to Skype (message says it can not connect to the server) it used to work fine for more than a year before that
making and receiving regular land-line calls still works fine
I have a working skype account on my laptop and I'v verified that I'm using the same login and password on the phone settings

As far as I can tell nothing has changed on the phone or base unit itself
I cannot upgrade the firmware as that connection also fails (can not connect to server message).
the only thing that has changed is perhaps that my internet cable modem was replaced by my ISP provider (Telenet) by a newer model that also has an integrated router, so I have eliminated my old wireless router.

The new internet cable modem with integrated wireless router has the EURODOCSIS 3.0 standard and I have no issues connecting other devices such as my laptop, printer or smartphone to it. I think I can even see an IP and Mac address for the skype phone in the list of connected devices.
the only thing I needed to enter to connect my other devices is the WPA2-PSK password
my phone is set to use TCP/IP and DHCP

I have done a several full resets through the phone menu and also disconnected hardware and phone battery pack to reset everything, all without any result.

Can anyone give me some idea what to try next?

here are my Phone specs
model: Philips VOIP8551B/36
firmware is V63.36
Skype SW version V1.9.183
ProductID: voip 855
Hardware Version: 1.0