Many of the internet users are always confused about the speeds.
In short, your ISP doesn’t commit or promise you any speeds. The ISP role is only to test and verify if the connectivity speeds are perfect or not from their node till your end.
What speeds you get for download or upload, completely depends on the server you are trying to download from or upload to.
Those are not owned by the ISP, so there is no way your ISP can commit or promise anything.
If any ISP does, they have no idea what they are talking about :)

Lets talk with an example –

Why am I getting only 256KBps internet when I am on a 2Mbps plan? Is my ISP cheating?

Answer/Explanation –

In reality, you are getting the internet speed your ISP promised. You are just confused between ‘Mbps’ and ‘MBps’.
Internet Service Providers advertise their speeds in Mbps(Mega bit per second) while download managers and torrent clients show the speeds in MBps(Mega Byte per second.)

1 Byte = 8 bits
1 Mega Byte = 8 Mega bits

So, if you are on a 2Mbps plan,
2Mbps=2048Kbps
2048Kbps= 256KBps = (2048/8)

Which is exactly what you are getting. For example, I am on a 10Mbps plan and I am getting 1.2MBps download speed which is exactly what my ISP promised.

I hope this finally gets your doubt clear about the internet and the measurement terms.