americredit terrible loan company, Internet

Based on what you have written here I guess we can figure that you are paying late. 

You signed a LEGAL agreement to make specific payments for specific amounts at specific times.  YOU are late in making those payments.  But because they won't refiance you, change the due date, apply your partial payments how YOU want, and continue to call you.  THEY are "lousy"..I'll just let you think about that for a while.

They are a Sub-Prime lender.  There is a reason you are with them, and that is because of your Credit History.  Either you have had issues in the past, or you have a lack of history. 

You will not find any loan company who will refiance their own loan.  Why should they?  They have a legal agreement with you at a specific interest rate, why would they change it?  If you want to refiance you need to find another lender who will pay off this loan.  But if you are late on this loan the chances of finding someone else who is willing to take this risk is not going to happen, unless you want to go farther down the Sub-Prime lender ladder.

As for asking your due date to be changed or having your PARTIAL payment applied to Principal.  You can always ask, but are not going to find may(if any) lenders who would do that either.   If you are having issues they may be able to give you a deferrment, but you need to call and ask them for it. 

The only reason they are harrassing you on the phone is because you are late.  Pay on-time and get current and an amazing thing will happen..they will stop calling.

YOU put yourself there with YOUR reputation of NOT paying YOUR bills on time.  Otherwise you would have been financed by a bank with a lower interest rate.  YOU have the subprime credit history and apparently you want them to make concessions to you because you are continuing your subprime ways of life.  You want them to refi...you want them to change the due date...you want them to take partial payments...you want a lower APR.  Quite obviously they don't trust you and nobody but nobody put yourself in that exact situation but you.  But, you don't have to remain there!  YOU put yourself into this and YOU can take yourself out!  Apparently you want all these concessions because you are having problems paying on time.  That's understandable but why not use your efforts to bring in more money so you can pay on time and get out of this subprime way of life?  Get a part time job!  Get a second job!  Its either complain, bitch, moan and whine or clearly identify the cash flow problem and CHANGE IT!!!  Be a child or be an adult.  The choice is YOURS!