You can reach them online here or by one of the ways below:
By phone
+1 877-373-6374 (US, Canada, Puerto Rico)
+1 781-575-3100 (everywhere else)
By mail
Computershare
PO Box 505000
Louisville, KY 40233-5000
By overnight delivery
Computershare
462 South 4th Street, Suite 1600
Louisville, KY 40202