Getting 'Access Denied' on multiple websites

As the title says, I am getting an 'Access Denied' message on multiple websites. The exact message is:

Access Denied
You don't have permission to access "website name" on this server.

The sites that I have discovered so far are homedepot.com, costco.com, and lowes.com. I have been getting the same message on all of the websites, besides the reference codes, which I will list below:

 Reference #18.15393717.1541289653.5c399d2 Reference #18.bf273017.1541289827.c064f1 Reference #18.84273017.1541289848.52e1d8 

My home's router is a Linksys EA9400 AC5000 Tri-Band MU-MIMO Wi-Fi Router, and my family and I have tried this on multiple devices, including a Windows PC, an iPhone, and an iPad, and I tried clearing my cookies on all of them, but it confirmed that it was a router problem, not a device problem.

What should I do to try and fix this problem?

Edit: Just rebooted the router, still not working. I'll upload screenshots as soon as I can.

Edit 2:

DNS:

With WiFi:

Without WiFi:

ipconfig /all

Edit 3: Added another picture to DNS Servers

Edit 4: Added ipconfig /all

Edit 5: homedepot.com works now, but the others still don’t

Edit 6: All of the sites work now, problem solved, I guess? Don't know why the websites were blocked though, that was kind of weird.

2 Answers

Solved itself on November 6th, don't know what happened here but all's well now!

Use this tool to check if your IP has been blacklisted and why. Then you may request an investigation.

I have requested an investigation from the Akamai team and voila! Problem solved :) The websites have been unblocked for me. I just wonder if it was Akamai or the UPC somehow? For all who encounter a similar problem, use this tool: