Why is my internet so slow at weekends during nighttimes?

[Herp]

I have DSL internet and my ISP is centurylink and i think im paying for 10 mbps which is $20 a month. Im trying to watch movies at night but i cant because of my stupid DSL internet the DSL light blinks for like 30 secs and the wifi light turns on but then after 5 more secs the DSL light starts blinking again and wifi light turns off. And the wierd thing is that it only happens in weekends during nighttime sometimes on friday nights idk why. i called my isp had a technician to come internet did improve but it didnt change my problem
My password is as secret as it can be, it pretty much came with the router its a bunch of uppercase letters and lowercase letters with a few numbers i have no idea how someone can get in my wifi that has such a complex password. My parents dont use the internet i am the only one in my house that uses internet and i always turn off my electronics and turn off wifi unless im using it. Basically i keep one electronic on at a time so i dont know how im getting this.
Also im not using netflix i know a free website with a lot more free movies than netflix and it doesnt really say anything about what internet speed you need