So each company can have up to three accounts depending on the pricing level.
A company is defined by the company name and the complete address
Is not the customer also defined by the first 6 digits of the account number?

Would there ever be two companies with the same first 6 digit account number
012345-000 ABC Shop 123 Fake Street
012345-001 ABC Shop 234 Next Street STE H

Finally, think about this and consider that it might work better for you

Account #
 Company Name Address 1 Address 2 Norm Pricing Discount Pricing Government Pricing
012345
 ABC Shop 123 Fake Street STE 204 012345-000 012345-001
056789 DBC Shop 425 Fake St 56789-002
051256 DEF Shop 100 Street 51256-005