Help, MODS! Unable to upgrade my account. Error code reads “sorry, account cannot be upgraded at this time”.

Unable to upgrade my account. Error code reads “sorry, account cannot be upgraded at this time”.
I keep getting what I assume to be IP address pool banned.
If I change to a mobile device, I can still login, but I cannot upgrade my account. I know that I’m not posting anything controversial, or disruptive or unkind. I think I should be able to do an upgrade, but it appears that I’m banned from doing so. I wrote to the webmaster numerous times, but never received a reply.
Any mods out there who can help, or at least explain why I can’t upgrade?

Thanks in advance