Every Time Creates A new Customer when a subscription purchased

I am using the Zoho subscription. I need help with the following.

1. Every time a customer subscribes to each and every plan with the same email address it is creating multiple customers with the same email. This is the problem we see the same customer is creating multiple times. How can we prevent duplication of a customer based on email address in Zoho subscription?

2. I want to show some custom fields to the admin but want to restrict these to a user. How can I do something like that?

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