Client service not replying to emails. Slow internet speeds.

Internet speed keeps dipping at night from 7pm. They had an agent call me when I complained and he sorted out the problem, but now it is back again. The speed is supposed to be 25mbps, but drops to under 1mbps. I emailed them, they sent me a ticket 2 days ago and I am still waiting for a reply. I rep**** personally to the agent via email as well, he never came back to me. I am paying for a 25 mbps line, not a 1mbps line. It is bad business practice not to get back to your clients. Fix the issue, or I will simply find another provider that does what I pay them to do.