You can find out more from this guys.
Physical address:
Merck South Africa
1 Friesland Drive
Longmeadow Business Estate South
Modderfontein 1640
Postal address:
PO Box 1998
Halfway House
1685
Contact numbers:
Tel: +27 (0)11 372 5000
Fax: +27 (0)11 372 5253