You could check to see if you were on a split pair by looking at the A and B legs on the rear of the master socket , if it’s not a ‘twisted pair’ as stated this may account for the poor upload performance…if it is a split pair , unless there is a serviceable ‘pair’ in the existing ( presumably 5 pair ) cable , the cable may need repair or replacement, and if it’s a DIG cable ( not ducted ) that could be a significant undertaking, and as upload isn’t guaranteed, you may need to make a case for it to be done .