@marcoblt
Why do you need phone connected to your line?
If the phone line is noisy or has a high resistance connection, then that will affect your broadband.
The lack of any current flowing through the wires due to the lack of a phone providing an occasional loop, causes oxidisation at any joints which causes the line resistance to increase. This does not show up on a normal line test.
There are quite a few people that do not plug a house phone in to check dial tone every so often. This can cause issues with broadband. Also, if one wire has become disconnected (quite common), then that will cause no broadband, constant disconnections, or a very low speed.
The solution is to get hold of a cheap (less than £5) wired phone, and plug it into the phone socket to see if you get dial tone.
Then dial 17070 (free call) and select option 2, quiet line test, and see if there is any noise on the line.
If you do not get dial tone, or there is noise on the line, then you need to report it as either no dial tone, or a noisy line. Do not mention the broadband problem, otherwise it will end up in the wrong fault queue, and take much longer to be fixed. There are plenty of people who can fix phone faults, but not as many broadband people.
Once the phone fault is fixed, then the broadband will get better.
You may find that the very act of plugging a phone in, and getting dial tone, fixes your broadband, as it breaks down any corrosion.
Also bear in mind Line rental is included in all BT packages
