How to contact the customs clearance department of «DHL Express Türkiye» in written form?

A DHL support person from the «DHL Express Türkiye» WhatsApp chat provided me with the kategori3@dhl.com email address.

1. For shipments ≥ 150€.

Talimat@dhl.com and sevilay.demirelli@dhl.com.

2. For shipments < 150€.

kategori3@dhl.com
Whats does mean «KATEGORİ 3» for customs clearance in Turkey?

How to contact the «Customer Satisfaction» / «Customer Demands» department of «DHL Express Türkiye» in written form?