Wikipedia doesn't have "customer service" per se; it isn't a business. However, there are a number of channels you can try to get help, voice a complaint, or find a contact for further dealings.
There are a few places you might try:
The fastest is probably the #wikipedia-en-help channel on Freenode IRC (Internet Relay Chat). If you're familiar with IRC and have a proper client, you can use this IRC link: < irc://chat.freenode.net:8001/wikipedia-en-help >
If you're not familiar with IRC, there's a helpful web interface for it at < http://webchat.freenode.net/?channels=wikipedia-en-help >.
The next is the Wikipedia help desk, on-wiki: < http://en.wikipedia.org/wiki/Wikipedia:Help_desk >
The last is by email. It's the most official, though still run by volunteers through a system called OTRS. It's confidential and can deal with some issues that a more public approach might have problems with. Send your email to info-en@wikimedia.org .