M365 Business Access Problems

TLDR: User failed to tell me they already had the domain associated with a personal M365 account. Screwed them out of the new M365 Business Account access after starting the domain setup process.

Situation: Can't access the newly created M365 Business Account for user's SMB. They failed to tell me they had the domain.com associated with a personal M365 account they were using for their SMB. So after creating the business account online and going through the domain setup. The account login is now screwed up. I can't seem to get a hold of anyone through the support on Microsoft's support page. It constantly asks me to login to the business account and we can't. Anyone got any insight or tips on how to get ahold of someone for business support? Thanks

No I don't work for an MSP and the user is some what affiliated with our medical facility but is independent in terms of business and IT. But I've been tasked to get them setup so we can manage their M365 for them. Because of cost.