One other thing, if I am reading your post correctly, it sounds like you have two wires jammed into one slot on the modular plug? If so, this is a real no-no. Field installed modular plugs are a crap shoot on a good day, and they were never designed for this. If I am misunderstanding this, please forgive me.
Maybe you can have the existing cable x-rayed, and find out what they actually did inside? Who knows what evils lurk beneath that cable jacket - I have seen some crazy-a** stuff over the years, especially where [pseudo] "hardware locks" are concerned.
Jim
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Speaking from a secure undisclosed location.
