Yes, you may certainly remove the lower front section to expose the duplicated test-socket, within.
If a wired telephone does not operate when plugged in there, you may carefully remove the VDSL2 interstitial plate (note: doing so will disconnect your broadband service) and try with a wired telephone plugged into the test-socket of the original
NTE5/A.
The results of your experiments should then be reported, on-line, to
BT.