Sudden broadband speed drop since last week

Hi all, I’ve been a Nexora broadband customer for over a year now. For the past week or so, my fibre broadband speed has dropped drastically — usually I get around 150Mbps but recently it’s been stuck under 20Mbps. I’ve rebooted the router a few times and even tested at different times of day but no luck. I’m not sure if it’s a fault with the line or something else. Anyone experienced this? Thanks!