Can loan companies keep adding more cost to my loan?

Read the loan documents, that's probably interest, late fees, etc.

Yes.

And it's nothing like you only gave them $26. If you only gave them $26, then they would have added more than just $84.

If it will cost too much "at this rate", then don't pay at this rate. Pay faster. Pay more than just $100 or pay more often.

It's called interest my friend. You probably borrowed money at a very high interest rate. It is charged until the loan is paid in full. Part of your payment goes to the current interest charge, the rest is applied to the principal balance of the loan. The faster you pay it back, the less interest is charged.

Review the agreement you signed for the terms & conditions of this loan.

That is how it works, welcome to the world of financing through those who know you are desperate. They will charge you the max the law allows. Better off going to your own bank for that little bit and paying them off, bank will give you a much more reasonable rate.

Read what you agreed to when you took out the loan.

All of this is explained in there.

like a credit card they are adding interest and other charges on the unpaid balance

It is probably the interest and late payment charge which is added to your loan. You must ask the lending institution to explain the charge. That will help you calculate the exact amount you owe to them and plan to arrange for funds accordingly.

Do you understand what "INTEREST" is?

Just call the loan co and ask how they came up with that amount

It is very difficult to fight with them They keep on adding other charges and the rate interest may also be more. Better try to avail a loan from a Bank and clear this loan.