Help: new VOIP - 'one way no audio' issue

Hello,
Looking for some guidance on how to proceed, please - but I recognise debugging VOIP issues is not without its challenges..

Short Story
New VOIP connection.
I can make and receive calls, but there is no audio for me, on either outgoing or incoming calls. However there is normal audio at the other end, where they can hear my voice fine.

Detail
ISP: A&A
Router: Technicolor DGA4135
Phone: Panasonic KXTG6801

I have just been connected to FTTP.
having been with A&A for years, I ordered through them, and took the opportunity to port my copper phone line away from BT and over to A&A also.

FTTP working well.
As the supplied router has built-in ATA, I connected my existing old style phone, via an adapter, to the FX1 port.
A&A helped with the Telephony SIP Network and SIP profile settings on the router, and it shows it as Registered on the router settings.

https://imgur.com/JjxZ8Mk
https://imgur.com/CBQxNoJ

Picking up the phone, there is a dial tone, and I can make and receive calls, but I hear nothing. Just silence. The other end of the call can hear me talk. So I think that's a 'one way no audio' issue.

Contacted A&A support, but they have just pointed me towards their support page
which I have tried to follow through, with no joy.

But I do find the router settings somewhat opaque in meaning, and not sure which I should be changing.

Here is what I have now:
https://imgur.com/wXETozp
https://imgur.com/swo5i6R
https://imgur.com/PfiRknd


Solution?
1. Is there a setting I have missed, that may just click everything to life?
2. Is my Panasonic phone not compatible? Should I just buy a Yealink T31 or T41 from ebay, and plug that in?
(Do direct IP phones plugged into an ethernet port on the router have less problems than old phones plugged into the ATA port?)

I only need a very basic phone, and just the ability to make and receive calls occasionally, so no fancy features required. But I do need it to work!

Very grateful for any advice.

For A&A VOIP I use a Gigaset N300 DECT base station and Gigaset DECT phones.

The N300 has an ethernet connection to a broadband router. I use this configuration at two locations. They both work OK.

Sounds like a codec issue. I've used both gigaset and fritzbox with A&A
Make sure your codec is set to g.711a

Do you mean here?
https://imgur.com/1oEBMdu

The only options are PCMA, PCMU and G729

In reply to a post by iDoccy:

Do you mean here?
https://imgur.com/1oEBMdu

The only options are PCMA, PCMU and G729

Yes. I believe PCMA is the same as g.711 a law. Is that what you had set?

A&a only support g.711a. anything else won't work (to be honest I believe it would stop the call from connecting as it should negotiate the codec during call setup)

Yes, set to PCMA

In reply to a post by iDoccy:

Short Story
New VOIP connection.
I can make and receive calls, but there is no audio for me, on either outgoing or incoming calls. However there is normal audio at the other end, where they can hear my voice fine.

without more information i am unable to help further

the issue is the RTP is being blocked, or the ATA is not sending out the correct IP, as the phone you call can hear you the outbound traffic is ok, your issue is the inbound RTP

Okay. What is the RTP and how do I unblock it?! : )

That is a UDP protocol
SIP initiates the call, but the audio is through UDP on a different port. Your router firewall is probably blocking it - why I don't know.
I did a google and found another page on Thinkbroadband forum, pointing here:
https://support.aa.net.uk/DGA0122_VoIP

you may need to SSH into the router to make this change if this model supports that...

And the forum page this relates to.
https://forums.thinkbroadband.com/voip/f/4689093-tec...