DSL out of sync, DSL Carrier is down

[#1]

Have been disconnecting all night, and when I check router logs, this stands out:
2002:9:8:12:4 DSL out of sync
2002:9:8:12:4 DSL Carrier is down
I don't understand anything in the router log. Internet has been disconnecting every 5-10 minutes since early evening.
Router: Solwise SAR600-EW
The router is around 4 years old, it might need an upgrade?

[#2]

Hi edmundjones,
I can see from the graph below that the connection is very unstable at the moment. How is your kit set up? Are you using any extension cables/sockets? Do you have a test socket?
Jojo

[#3]

The router is plugged into the test socket (which was installed about 2 weeks ago by BT).
The disconnects are becoming much more frequent, struggling to keep a connection for longer than 10 minutes today.
2002:9:8:12:2 DSL out of sync
2002:9:8:12:2 DSL Carrier is down
2002:9:8:12:3 DSL in Sync
The above appears in the router log during a disconnect. The DSL light switches off, and then flashes. Then the DSL light goes solid and the internet light comes back on and it works.
I initially thought it was related to use of the telephone, but after unplugging the telephone for much of today, there has been no positive change.
EDIT: I was advised by Solwise (router provider) to perform a firmware upgrade which they walked me through, the router has been plugged in for 7 minutes, and in that time it has disconnected three times.

[#4]

Hi edmundjones,
I can see that you've raised a fault. I'd wait and see what they come up with.
Jojo

[#5]

Yes, I've been told that's all I can do. I was told by a member of your technical support team that I have disconnected 58 times since 7pm last night, which is beyond a joke.

[#6]

Hi there,
Looks like we're now at the stage where an engineer visit is required to further the investigation, please could you reply to the ticket advising when you'd be available for an engineer to attend and we'll get that sorted for you?