investor problems

Hi.We have a small business that operates under a company contract. When our contract expired we made sure to return all the capital to the investors and they agreed (No papers were signed and we just explained it to them.) After a year, we were able to get a new contract from another company. Now the investors are back asking for their share of interest. We're really shocked because when they gave us the computation it shows there that the capital we returned were just their share during the time we don't have any business. And now we are still in a lot of debt. Do we still need to continue "paying" the investors?

This are my father's "friends" and I want to stop giving their share since their the only ones profiting from this.

Thanks in advance.