Hi Oliver, welcome to the community! thank you for posting to bring this to our attention!
Sincerest apologies that you are having these issues with your landline connecting to your mothers number in China.
I will happily look into this further for you, we will just need to send you a PM to confirm a few details so we can investigate.
You will find the PM in the top right corner of the page in your Inbox.
We can return to the public thread with an update as soon as possible.
All the best!
Molly