HORRIBLE connection for a week from sky!?

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I usually get 1 mbp/s when downloading a item on steam but its been reduced to 100 kbp/s! I am using sky unlimited connection, they promise to give me around 11 megabits per a second instead I am receiving 1.4 megabits per a second. I called them up and they have horrible costumer service which didn't help at all. I checked my sky maintenance connection speed, it says its giving me 11,000 kbp/s which is bullshit because all my devices are running slow as fuck! Sky is a disgrace, do you know anyway I can fix this problem? I heard switching wifi channels but I don't know which one to switch to. I have restarted my internet serveral times and my router has not been moved at all and then it just went to shit one day. They said they wont cap our connection when we brought unlimited so i don't see why we are only getting around 200 kbp/s. When i download something on steam it goes to 1.1 mbp/s then after 20 seconds it drops to 40kbp/s This is shocking i don't know what to do!