Fast Download speed but slow Streaming! Need help.

I used to watch youtube at 480p without any problem with my 2mbps plan.
But from couple of days i am getting slow speed while surfing and streaming. Cant even watch at 240p.
I know i should have contacted my ISP first but my download speed is working perfectly as it should be (what should i tell em).
The problem is only occurs while streaming and sometimes surfing.

What i did for trouble shooting:
Tried different browsers.
Tried different device.
Checked no one is using wifi while i am streaming.
closed all the software that can use internet like spotify etc.
Restarted my router.

Cant even watch in my android YT app in the night while everyone sleeping.

also Speed test dont show the correct result. Most of the time they dont get close to 2 mbps, but still get the right speed in download manager.
Its like affecting everything except downloading.

There is lot of use of youtube in my house (but mostly one person do it at a time).
My plan is unlimited. Could this be my ISP doing it on purpose because of the lot of use? I heard somewhere about that they can do it.
What should i tell them when i contact their technical team?

they can throttle the traffic of course by different traffic types, but not without letting you know it first or maybe there's something referring to this in the contract you signed

i use 2 internet connections, an unlimited cable connection and i also have a 4G mobile connection with monthly 30 GB daytime + 100 GB night-time data plan, if i reach any of those, the traffic will be throttled for the rest of the billing cycle, but not everyting, it affects only the bandwidth-intensive traffic like torrent, youtube, while normal browsing, emailing is still unlimited

so just ask them what's up, don't make a big deal out of this, they will know what you're talking about, but from the looks of it, it's throttling, so you can either accept it or move to a different provider

Have you tried updating Adobe Flash? I've had the same problem earlier and this is how I solved it.

Open Chrome and type this in the URL box
Scroll down and disable Adobe - http://prntscr.com/96w9vu

Install the latest version of Adobe Flash and then re-enable it in Chrome.

Comcast claims that they do not cap accounts. I don't agree. I had the same issue. I had to call comcast so many times over the course of a few months before they finally fixed it.

I was like, look, we signed a contract for 2 years and you are not living up to your side. I am not getting the minimum speeds in the contract. So the guy finally fixes it. I said, oh, that worked. What did you do? He said he changed the frequency. HUH? I said can you explain? He wouldn't.

Also, when I had a private guy come check the power line, he found 3 limiters on my cable line. Yeah, they try to restrict you. Don't let them pull that bull.