Whether or not you decide to pursue a refund, I would strongly recommend that you replace the internal Geoport Express software modem with an external hardware modem. But to do so you need to follow a few simple steps.
Apple's advice on this step is as follows: "If you need to use the external modem port, the internal modem must first be removed. Instructions for installing a card into the communications slot are included in the Macintosh Performa User's Manual. You can follow these instructions for removing the internal modem as well. Although such cards are typically user-installable, you may want to contact an Apple-authorized service provider for assistance with this procedure."
The procedure for removing the modem is not difficult, but if you are uncomfortable with installing hardware you may wish to seek assistance. Daria's site contains some good advice on removing the internal modem.
Apple recommends deleting all the Telecom software and extensions to avoid conflicts with your new modem's software. For a comprehensive list of the files you should delete, visit the Apple Tech Info Library and read Article ID# 20973.
A quick fix (though not a real solution to the problem) is to connect the external modem to the printer serial port on your Performa. Then open the Modem Control Panel, select your modem type, select the printer serial port, and you're finished. This does not require you to remove the internal Geoport modem. I would recommend this as a temporary solution for those who need a functional connection to the Internet right now. Obviously this fix requires you to disconnect your printer, so it is not a very desirable situation for most computer users. The real solution requires you to remove the internal modem because the modem serial port is inactive until the Geoport is removed from the Performa.