You can update/change your registered mobile number with your Giottus account. Write an email to support@giottus.com MENTION THE REASON FOR CHANGING THE REGISTERED MOBILE NUMBER and complete the following verification process.

1. Reason for changing the mobile number.
2. New Mobile number and current registered mobile number.
3. In a white paper write 3 details,
o Giottus
     o Your registered email
     o Present-day date

4. Hold this white paper and your PAN Card and take a photo along with yourself. (Check this sample image for your reference).  

5.    Our team will contact you further to complete the process.