There can be several reasons.
One of the problems we face in our region of Turkey is relatively slow internet speed. Especially during times when the government is interfering with it. Often it's a hard enough job just trying to keep the lights on.
No not with TTNet or Ookla etc. because most of those are rigged in favour of the ISP's and it is important what location you are checking with, it is no good checking with say Izmir if the website you want to connect to is hosted in America. Always check internet speeds with an independent tester like this one http://testmy.net
If you are net getting the download speed you expect or are paying for contact your ISP and politely complain. But note: Most ISP's including TTNet have what they call a "fair usage" policy, mine is 50 Gb, once I exceed that in a calendar month they reduce me down to 1 Mbps, you can check your usage yourself by logging into your account.
If too many people are using your connection at the same time you will have problems. Make sure a neighbour isn't leaching off your bandwidth, tell the kids to get off those online games, ban the wife from watching Corrie while your footie is on (good luck with that one), but basically steady it all down and log of Facebook for crying out loud.
Absolutely nothing you can do about that, you've got more chance of getting the wife to turn her Coronation Street off.
Contacting me, there is nothing I can do about any of it!ALL FAQ's