Is Someone Siphoning My Internet? Help Needed with Sudden Slowdown

I’m facing a perplexing issue with my CenturyLink fiber internet, and I could really use some expert advice. I’ve been enjoying high-speed broadband in my home in the Pacific Northwest for about nine months, typically experiencing download speeds around 950 Mbps and decent upload speeds to match. However, out of nowhere, my connection has dramatically dropped, with speeds plummeting to a frustratingly low 4 Mbps.

The inconsistency of the situation makes it even more confusing. While speed tests occasionally report speeds of 20 Mbps, or even 100 Mbps, there are frustrating instances where only 1.5 Mbps shows up on the radar. To make matters more puzzling, my upload speeds remain impressive, sometimes hitting the 900 Mbps mark, while downloads feel like a trickle.

When I reached out to CenturyLink for assistance, the technician conducted several diagnostic tests but found nothing amiss with the connection. He sent another technician to my home, who thoroughly inspected the newly installed line, replaced my modem, upgraded the Optical Network Terminal (ONT), and even ran new Cat6 cables—all to no avail. We tested everything via a direct Ethernet connection, but the situation only worsened with a Wi-Fi connection. The technician kept inquiring whether I was using a Virtual Private Network (VPN), but given my limited understanding of VPNs, I assured him I was not utilizing one. Ultimately, he left scratching his head, and when I called tech support again, their response was similar: “Everything seems fine, but are you sure you’re not using a VPN?”

Additionally, I’ve noticed a troubling trend in Google Chrome—I’m prompted with captchas that indicate suspicious activity when performing searches.

This has led me to wonder: Is someone possibly accessing my connection without permission? Am I just missing some crucial piece of information or an indicator of what’s wrong? I admit I’m not the most tech-savvy person, and I’m unsure how to proceed.

Update: I’m using Macs for my devices, which may play a role in the issue.

If anyone could provide insight or suggestions on how to tackle this situation, I would greatly appreciate it! I’m eager to resolve this mystery and potentially restore my previous internet speeds. Thank you for any guidance you can offer, and I’ll be sure to keep you updated as I continue to investigate!