I don’t even use the telephone, but my broadband is still slow or unstable

It is an increasingly common case that customers use their fixed telephone line purely for the broadband and don’t even have a telephone plugged into it, preferring to use a mobile phone for voice calls. If the broadband is becoming slow or unstable, it is definitely advisable to plug a telephone into the socket to check the line is working (see question further above about broadband working but phone line not) or crackly. Both of these telephone line faults will certainly cause a huge drop in broadband performance.