I am getting the following error in my customer integration :
Error: Another process has added the 'Customer' record. Your changes will be lost.
We do not have this customer number in customers or vendors in this tenant. When I go in to manually add the vendor I get this error:

The Customer ID identifier is already used for another business account record (vendor, customer, employee, branch, company, or company group). 
I have gone through vendor, customer, employee, branch and company (don’t have company group that I know of) and none of them have this customer number.
We do have multiple tenants and customers/vendors do occur in multiple tenants as this one does, but with the other customers we did not have any issues adding the customer into this new tenant.
Any suggestions are welcome.