How much to charge ?

I just started recently working with an investor that needs help translating calls . It’ll be several calls per week but won’t be more then 20 mins at least 2-6 times per week, it just depends. They wanted to pay me 300 for helping them close a contact which I didn’t think was much given that it’s been about 2 months of this . So in the future I’m looking to establish a better pay of either per minute, per call or per week. Just trying to go the right way about it