Your ISP will not be responsible for your WiFi speeds, they are responsible for your broadband speed to the modem/router/hub (whatever they call it). WiFi can be subject to all manner of interference from things such as microwave ovens and your neighbours using the same WiFi channel as you (not on your connection more like listening to the same radio station). To check your speed accurately you need to connect a computer by a cable directly to the router and then do a speed test (well several at different times throughout the day). If they all show a decent and similar speed the problems lies in the WiFi, at which point you need to start thinking about what might be interfering and whether you can manually configure your set up to use a different channel to see if that helps. Also, do you have dual band WiFi, normally 2.4 & 5Ghz, 2.4 tends to get more interference but has better range so if you are close to the router try the 5Ghz connection to see if that is better.