about the first question (if it's free).
Since the author of repository it's under of GNU (in the repo has the link, but if you didn't read it or see it here's -> https://github.com/PHPOffice/PHPExcel/blob/master/license.md).
Second, about your continue 2 error, you need check first which version of PHP you're running, those continues issues are very frequently in some old libraries (mainly this one the last significant update was 6 years ago).
If you check the issues of Github you'll see there's an exact bug issue opened about what you're asking here https://github.com/PHPOffice/PHPExcel/issues/436.
Ok, but what's the solution?!
Well, you have 2 simples solutions:
1 - Use another library or create yours.
2 - Try to fix the issue.
Particularly if I was you I chose the first, and now when you get some new library/plugin I strongly suggest you before download it check the issues in the repository to avoid has those weird bugs in your system.
If you anyway choose for some reason keep going with this one, try to fix it and open a PR.
As per documentation, you can fix easily https://php.net/manual/en/control-structures.continue.php and just compile again the library and it's done.
