Got a voice mail to discuss my National Grid bill

Wanted to discuss my National Grid Bill and insisted on having my acct no.
Almost an nonunderstandable accent.

This is a call trying to get one to change electricity providers. The accent is barely understandable. I asked several times that they send me written material on their plan, but they never do. They phone 3-4 times per day for weeks now. This is obviously a "slamming scam".