Postingan ini akan membantu Anda untuk menghapus data customer dengan cepat di Database, pastikan ini bukan data customer di production ya.

SET FOREIGN_KEY_CHECKS = 0;
TRUNCATE `customer_address_entity`;
TRUNCATE `customer_address_entity_datetime`;
TRUNCATE `customer_address_entity_decimal`;
TRUNCATE `customer_address_entity_int`;
TRUNCATE `customer_address_entity_text`;
TRUNCATE `customer_address_entity_varchar`;
TRUNCATE `customer_entity`;
TRUNCATE `customer_entity_datetime`;
TRUNCATE `customer_entity_decimal`;
TRUNCATE `customer_entity_int`;
TRUNCATE `customer_entity_text`;
TRUNCATE `customer_entity_varchar`; 

Setelah itu lakukan reindex, semoga bermanfaat.