Before you rant about your slow speed to Maxis Customer Care, please be reminded that speed is affected by few factors:

1) Your device:
-You can't expect it to have 20Mbps when your modem's capability is just running max up to 7.2Mbps.
-You might be having a faulty modem, try switching your SIM card with other modems

2) Your signal coverage:
-If you are not within DC-HSPA+ coverage, then don't expect to have 20Mbps of speed. Be contented with just probably 5Mbps speed, that's probably what your tower is capable of. I know someone who was already running in joy though he only gets 2Mbps on his Maxis. Yes, he is in Mukah, Sarawak.

3) Congested with other users:
-If you are unlucky and you live in an area where there are a lot of similar users like you, be prepared with network congestion. Everyone is fighting with you. Though you might be living in a non-urbanized area, that doesn't mean your area will have good speed. All telco providers will do survey first before doing bandwidth allocation, if you area has low density of users, they will not allocate more speed to that tower. So can't do much thing about this.

4) Timing:
-Avoid performing download activities during golden hours (7-11 p.m.), this is the period where those working folks are back to home and start jamming the line. Be considerate with others. You could queue your downloads to start only after midnight when they go to bed.

5) QoS:
-Check your QoS first, it could be your area is only capped to 2480/2480.

OK, after checking through the above steps and you are still very sure that something is wrong with your connection and tower. Login to your Twitter account and start tweeting the Maxis CS. Follow them @MaxisListens and they could respond to you quite swiftly. Lastly, be patient and they will fix your issue soon!
Before I forget, I think it is worth mentioning here that Maxis blocks P2P port in order to provide better speed to other users. Let's not forget there are other needy users out there depending on this connection to do their work and etc. So, don't hog the connection with your P2P activities. The port will only be opened at 1.00 a.m. - 7.00 a.m. or 3.00 a.m. - 7.00 a.m., depending on your area. So, plan your download activities wisely.

Of course this can be bypassed with VPN or SeedBox but I'll not further drill into this part. Check out yourself and don't ask me or us how to bypass it.

-Credits to fruitie for the info posted above.