Here are some options for filing complaints against package-delivery companies.
If you feel there has been a violation of DOT regulations, you can file a complaint with the Federal Motor Carrier Safety Administration (FMCSA) at 1-888-DOT-SAFT (1-888-368-7238).
Motor carrier federal regulations can be found in 49 CFR Chapter III.
The FMCSA home page is http://www.fmcsa.dot.gov/
Otherwise, your best option may be to file a complaint with the Federal Trade Commission (FTC). You can find their complaint form at this site.
The FTC's home page is: http://www.ftc.gov/
You may also want to file a complaint with your state consumer protection agency. You can locate your consumer protection agency through this page.
Finally, you can file a complaint through the Better Business Bureau.