If your Internet Service Provider (ISP) support team are telling you that your line is fine, and everything is working as expected, you may need to do some homework about your service.
Standard broadband over telephone lines degrades in speed the further the line is from the telephone exchange (in cabling length). While most deals are advertised as, for example, 'up to 42Mb', most telephone lines will be rated to achieve slower connection speeds. Run a broadband speed test on your line. Ensure that the speed you're told to expect is actually higher than the speeds you're experiencing - it may be that you're already achieving the fastest speed your line can accept no matter if you live in a City or the Country.
Make sure your ISP hasn't capped your speed because you exceeded the limits of your monthly usage allowance or traffic management policy. Many ISPs now reduce your speed rather than charging you for exceeding your allowance. You should be emailed a warning if you exceed your usage allowance, however if you've simply exceeded the traffic management allowance (often in place at peak times) you won't be informed, your speed will simply drop for a fixed number of hours (or until the peak period ends). Your ISPs website should give you details of any traffic management policy in place and inform you of the effects of exceeding your usage allowance.
Make sure all phones and faxes are connected via a microfilter. Microfilters prevent other devices connected to your telephone system from interfering with your broadband signal. Every device connected to the phone system should use a microfilter. If you still have problems, unplug all devices and gradually add each back until you identify which causes the problem. If you're using free microfilters supplied by your ISP or with your router, consider paying for more expensive microfilters with good user reviews - it's possible one or more of your filters is faulty or of poor quality.
Plug your modem/router directly into the Master Socket. A Master Socket represents the first / main point inside your home or office for connecting to Openreach’s outside copper cable, which makes it the best socket for connecting with your broadband router. Most master sockets have a split across the front plate. The lower section of the plate can be unscrewed and inside is an engineer's test socket. If you remove the lower faceplate it will disconnect all the extension wiring in your property. You can then connect your modem/router using the test socket. If you get an increase in speed then your internal telephone wiring is causing interference that is lowering your speeds.
Poor quality extension cables are probably the number one cause of poor broadband speeds. Extension cables can massively increase interference on your line and cause broadband speeds to be lowered. The simplest way to solve the problem is to ditch the extension cable and connect the router directly to the Master phone socket and then use a long ethernet cable to connect your computer to the router (these can be purchased in any computer store and cost around £1 per metre), ethernet cables will not degrade the speed of your connection.
Use a new, high quality cable and ensure you use the shortest cable possible - tangled and coiled telephone extension cables can cause interference. You can easily test if your extension cable is the problem - connect directly to the master socket, if this causes no improvement in connection speed, it's unlikely that the extension cable was the problem.