Verb conjugation of "supply" in English

The billing of additional working hours is not justified, since it was our request to download the software and wait for the new version. They have admitted the error of the translation.
We have learned that some tenses, such as Present Tense are easier and not as complex as others. Is that right? In my opinion, tenses in English are much easier than in the Spanish language.
I would be pleased if we can still keep the contact alive. In the future I will have more time to write emails in Spanish. At the moment I just can't. Sorry for being so direct but this is the truth.