how should i call and complain to a call center agent?

The first thing that I have to ask is... Was it custom ordered, colored specifically to match your walls?......

That aside, I would be prepared with appropriate information (and a bucket full of patience!) before you call. Because most people plan ahead to "color coordinate", I'll assume it was a specially ordered appliance. Be prepared ahead with:

Your receipt, the name of the company that did the order for you, the sale's associates name if possible, your warranty information/serial information, and the conditions under which you purchased this item. With all that in tow, remember...

1. Many call center employees handle calls for more than one company
2. Many call center agents have a specific script or set of questions dictating
to what they have to say and/or ask.
3. They have rules and policies they must adhere to - be prepared for them to NOT
break these rules. Getting upset if one doesn't is pointless.
4. Most call center employees have never stepped foot into the business for
which they are taking the call, so expect that they might have only a limited
knowledge of a particular store's policies.
5. Expect a wait time and expect that you might even get an accent that you
can't quite comprehend.. Several ways around and to remedying that though.
6. Be polite, even if they're not. If you think that their behavior is less
than professional, you can try to call again in the hopes of getting a different
agent on the line or ask to speak to a supervisor.

Other than that, the rest is simple - You paid for a product that was supposed to be specially ordered that did arrive with the specifications you supplied and take it from there. If you didn't specially order this item and just went to a place and purchased it... (A) I'm not sure why the retailer won't just take it back since it came from their sales floor... and (B) why you didn't realize this ahead of time.

Good luck.