If it was me, I would get a couple of the grease filled connectors of the type Telstra blokes use, and a small wire cutter and pliers.
Bung them in your pocket and ask whoever has the key to open the cabinet for you "as you need to take some details for a service tech."
Then do a quick snip and crimp, bung it back in the bag and it's all good.
Actually - if it was me, those locks are usually pretty easy to open.........
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When I bought my house it had ruddy awful phone reception.
Ended up finding a bunch of dodgy joins in the ceiling and garden.
Telstra didn't want to know / quoted outrageous rates to rectify.
Asked the comms ombudsbloke for info regarding dodgy work by previous owners, they came and had a look and couldn't give a rats freckle.
I renewed the dodgy cables myself, using all the same gear Telstra use.
Still had a crook line
Telstra fellas did on-line testing and bounced a signal down the line.
They determined that when the area was wired for cable telly, the cables were dragged through the Telstra conduit - which ripped the insulation from the phone cables, causing them to short out.
Telstra ended up running new cables between the pit/post and my place at no cost and lotsa apologies.
stephen