I just opened my copy to check. In Help>About it's still registered to Giveawayoftheday and I can't make it display any trial notices so looks like no problem here.
Could you (or someone else in your home) have inadvertantly clicked the "check for new versions" option under Help? That option is separate from program settings and it appears to only activate that function when the option is specifically clicked on. The program doesn't "phone home" on its own.
How it happened probably doesn't matter at this point though, you're already at the trial version. Below are links to some freeware alternatives that work just as well, splitting files with no conversion involved so no quality loss. Hope you find one you like from the list. The first one is probably the most widely used and it's quite good.
MP3 Direct Cut:
http://mpesch3.de1.cc/mp3dc.html
Mega MP3 Splitter:
http://digilander.libero.it/mega27/mp3split/
MP Trim:
http://www.mptrim.com/
MPEG Audio Scissors:
http://www.tfm.ro/index.php/MPEG_Audio_Scissors
MP3 Split:
http://www.merlinsoftware.com/mp3split/
Audiobook Cutter: (works on all MP3 files, not just audio books)
http://audiobookcutter.sourceforge.net/
MP3 Extractor:
http://www.mp3extractor.com/