That is a CWSS unit (Copper Wideband Serving Section), so you are a BT Business customer probably running ISDN30. You have a problem on the copper pair serving your premises, that is why you are losing your phone calls. I used to work on these circuits before I retired.
This is a BT Retail forum so you will need to report this to BT Business. You should have been given a number to report the fault to.
You could try the ISDN30 people, but they will only see the losses, and will refer it back to the Private Wire team.