why is my upload speed slowing down so much lately?

i have had the ultimate package for roughly 1 and a half months now. since then i have had to call service on my internet speed 3 times including the day after i had the service installed. 

i have had 3 total visits from techs, the first 2 being from the same guy who was fantastic, found the packet loss problem, called maintenance on the line, and the issue was fixed shortly after.

after that though the upload speed is faltering again, i had my third visit from a tech who chose to not believe what i was saying and say that every manner in which i was testing my internet speed was unreliable and not supported by their testing specifications, who also only checked the connection at the modem and not the signal strength or at the cable junction box for my apartment. 

i still believe that my connection is not stable or reliable and i need it for work.