Slow internet speeds and dropping connection

Question

hello, I am making this post on behalf of my dad, for a good few months (5-6 maybe even longer) we have been experiencing slow internet speeds and a dropping connection when ever the phone is picked up. when an incoming call is answered some or all devices connected to the internet drop out for a second then come back online, the connection does not completly disapear but causes any voice chat, streaming or gaming to disconect. We have BT wireless phones (not sure what exact type) which we have had for a few years. they are connected through an ADSL filter which as far i can remember has been there for years. We have a netgear DG834GT router which has also been there for a few years. I went onto its settings and got this information, not sure if its usefull or not.
System Up Time 42:18:47
ADSL Link
Downstream
Upstream
Connection Speed
1760 kbps
448 kbps
Line Attenuation
61.0 db
31.5 db
Noise Margin
13.1 db
13.0 db
 I also got this from the BTW speed tester
1. Best Effort Test: -provides background information.
Download  Speed
1.24 Mbps
0 Mbps
2 Mbps
Max Achievable Speed
 Download speedachieved during the test was - 1.24 Mbps
 For your connection, the acceptable range of speeds is 0.4 Mbps-2 Mbps.
 Additional Information:
 Your DSL Connection Rate :1.76 Mbps(DOWN-STREAM), 0.45 Mbps(UP-STREAM)
 IP Profile for your line is - 1.25 Mbps
I hope this is enough information to figure out what is going on with it.

Answer 1

put everything back as it was and this is what it looks like now:
ADSL Link
Downstream
Upstream
Connection Speed
160 kbps
448 kbps
Line Attenuation
61.5 db
31.5 db
Noise Margin
19.9 db
12.0 db
also while i was doing that i did i quiet line test and both myself and my brother listened to it and agreed that there was buzzing/static