I came upon this thread waay too late unfortunately.
I was in your position, rats' nest of internal wiring. The way I fixed it was to call my phone service provider and ask them to book an engineer visit to carry out “change point of entry”. This got me a new drop cable to the other side of the house, nearest corner for the run, and the cable came straight into the house exactly where I wanted it, to a lovely shiny new NTE5a and as near as dammit zero length of house-internal wiring, no extensions and a free BT Pressac faceplate-type (SSFP) microfilter that was in the van.
So all tidied up, lovely and neat. BT Openreach man did a smart job which I was very happy to pay for.
Strongly recommend this as the stock plan, the way-to-go, is just to remember the key four-word phrase, “change point of entry”, the bypass to get over all confusion and messing about. BT knows exactly what you need and it has a price tag on it. (Nothing to do with your ISP, unless you pay them the line rental too, it's whoever you pay POTS line rental too, whoever sends you a phone bill.)