I've convinced the guy to come and replace my modem in the morning. Let's see if he turns up. I've also escalated the issue on a higher level to try and get some answers before I give up and go to Nayatel.Just for the sake of doing it, replace the modem.
Also, post a screenshot of your line stats.
Here are my line stats (VDSL 2)
Downstream Upstream
SNR Margin(0.1 dB): 108 73
Attenuation(0.1 dB): 208 0
Output Power(0.1 dBm): 145 94
Attainable Rate(Kbps): 79750 22457