Rickles:
The ringer has no branding, just a small round (40mm diameter) unit with a BT plug on the back.
OP if its REN3+ as @sbiddle suggests you will need a ren booster like one of these
https://uk.rs-online.com/web/p/telephone-accessories/2079519/
In which case you will go
Ultrahub > REN Booster > Internal Wiring
EDIT: That product appears to be discontinued but there will be other similar products around