I'm an IDM user, I used to have a cheap technicolor modem and suffer from low SNR (around 7 to 9 db at night), I managed to increase it up to 30db by changing the protocol used to communicate, in my case I logged in to the modem using Telnet and managed to change the protocol to another with lower downstream rate, in your case choose a protocol with at least 8mbps as downstream, reducing the overall line designated capacity will increase the signal quality
https://en.wikipedia.org/wiki/Asymmetric_digital_subscriber_line#ADSL_standards
https://en.wikipedia.org/wiki/Asymmetric_digital_subscriber_line#ADSL_standards