wild speed variationn

I am looking at a friends broadband who is on the 01603 and was connected with pipex. Prior to january speed was stable 5m since january there have been multipal calls speed now average 1.6m today after some time we located the first connection point which has a new overhead and a new internal master socket and wiring we did however find old cables still connecttted at the incoming junction, disconnected these speed 2m but when measuring the line speed it varies wildly from1/2m to 5m download upload stable at 1m anyone suggest why the download speed shwould be so unstabe? we have conncted router direct to oncoming line no change, despite multipal calls no help from supplier

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