I'm not sure I fully understand your situation, but based on what I think your problem is, here are a few suggestions
1) Pull your most recent 401(k) statement. Hopefully that will give you information on who the trustee is for your companies 401(k) plan and contact information.
2) Call the bank and ask to speak to the Relationship Manager or the Administrator for your companies 401(k) plan.
3) Calmly explain your problem. Tell them that you requested a distribution (or loan or whatever your specific situation is) from the plan on such-and-such a date. Explain to them that you never received those proceeds.
4) Confirm you mailing address with them and request that the a stop payment be issued on the original check and that the funds be re-distributed to you. Rather than having the funds sent via check, you might consider giving the bank your checking or savings account information and having the funds "ACHed" into the account or if time is critical, have the funds wired to your checking or savings account. (Caution though there may be a wire fee assessed to you)
If the bank is unable to provide the assistance you need, you might ask them if the recordkeeper is the party that could help you. If so, then basically ask the same questions.
If these steps don't help add a new post and I might be able to give you some additional avenues to pursue.
But my ultimate suggestion would be to speak calmly, give as many of the facts as you can, don't get frustrated if you have to repeat your story to several people (most likely the person on the other end of the telephone is just trying to get you connected to the right person or department), be firm, and be tactful.