Unfortunately VM don't have a customer facing email address, and you will need to contact VM directly as the Forum Team don't have access to enable them to change your package.
If you don't want to be tied up on the phone 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.
You can also call 150 from a Virgin landline, or 0345 454 1111, options 1,1 and 4 (Changes to your package) butbest to call between 8am and 10am to avoid call queues, or late afternoon around tea time
The Service you do for others is the rent you pay for your room here on Earth - Muhammad Ali