Customer insists we use TeamViewer. EULA violation?

A customer is insisting that we use TeamViewer to provide after-sales software support to them. They are licensed commercially; we are not - unfortunately we use a different solution. The customer has created a user account and credentials for us to log in remotely, i.e., we would be using TeamViewer under our customer's commercial license, albeit with their permission.

We are not an affiliate, subsidiary, sister company, etc. of the customer.

Is this a violation of the EULA?