Ok it is the same error. I think you need to find a way to get the proxy configured on your computer to access a cran repo. Either by your admin team directly, or by you if they provide you with the information.
About the cran mirror, I suggest using https://cloud.r-project.org/ (Automatic redirection to servers worldwide) that you can configure in the call of install.packages or using options(repos = c(CRAN = "https://cloud.r-project.org/")) before.
Otherwise, it seems you are working in an offline environment. You can ask your admin team if they can provide with an internal CRAN mirror using linux rsync tool for example. (it is what we have at my place of work)
On the R side, you have minicran that can help you build a local cran mirror with the package you need, on an online computer. Then you transfer this repo to your offline server and connect to this repo for installation.
See the vignette for help on this solution.