Cannot get onto Apple Developer Forums

You can simply let the Safari membership term run out, as it doesn't look like Apple has given people an easy way to do this. Your best bet at cancelling it immediately though is to call Apple directly at 1-800-633-2152 and ask for them to cancel it.

I have run into a similar issue like this before when I was taking my ACMT certification. Essentially I created an iCloud email account and tried to use it to take my 10.9 Apple Certified Associate certifications fine but when I went to take my ACMT and log into GCX it told me I could not with that Apple ID.

After calling Apple and being on the phone with a few different people for a few hours they came to the conclusion that I needed to create a new Apple ID in order to take my ACMT. Luckily I was able to transfer my certifications over to my new Tech ID just fine.

Sometimes an Apple ID can get messed up in there system and there is nothing Apple can do about it. I would create a new Apple ID and renew your developer account with it.