Unfortunately you need to contact VM directly as the Forum Team don't have access to enable them to change your package.
I'm afraid there isn't a customer facing email address either.
If in the the upgrades and offers section you see an Oops something went wrong message, it's because you either already have a discount, or because the package you are on is no longer sold and requires extra manipulation by agents to change the package.
If you don't want to be tied up on the phone then you could try the text messaging service. Just send a text with a description of regrade to 07533 051809. Your message will go into a queue and a representative will respond to you as soon as possible. It may take a few days.
I know it's difficult now, especially with Covid, but could you possibly get somebody to sit with you if you call again? You could answer the questions to pass DPA and then pass the phone to them to negotiate on your behalf. Then you just pop back on to confirm if you are happy to go ahead with the changes.
The Service you do for others is the rent you pay for your room here on Earth - Muhammad Ali