If you don't receive a reply within three days, you can re-contact the customer service department.

re-contact 是由前缀 re-（表示"再次"）和动词 contact（联系）组成的复合动词。re- 表示重复动作，contact 意思是"联系"。re-contact 合起来表示"再次联系"或"重新联系"。