calls not connecting properly

[kjmj]

Hello,

I have a PAP2TNA and it has been working almost flawlessly until this morning.
When I phone certain phone numbers, nothing happens. However those recipients have advised me that their phone rings and when they answer there is no audio. These phone numbers I am having trouble with are numbers I call on a daily basis.
Inversely, if they phone me back, the call rings through but neither party can hear eachother.

Strangely, this only affects some numbers. There are other numbers that connect without a problem.

When I check the call log, it says normal call clearing on both.

I have not changed anything on my firewall, nor has anything been changed on my PAP2TNA.

Any suggestions?

Thanks