I cannot findthink of anything to writell. I cannot think of anything to write.

Please close this matter by finding a positive and sensible way. Please close this matter by finding a positive and sensible way.

Otherwise, believe meit or not, we will do whatever is necessary. Otherwise, believe it or not, we will do whatever is necessary.

"Believe it or not" is a set phrase, and I think it sounds more natural in this situation.

We worked with you since 04.09.2021 and we just learnt you are the company's legal manager from a notarised letter. We worked with you since 04.09.2021 and we just learnt you are the company's legal manager from a notarised letter.

We don’t understand why you hid that you are the manager of the company from us while the process was being managed badly. We don’t understand why you hid that you are the manager of the company from us while the process was being managed badly.

I request you to cover our financial damages by showing a compromising position. I request you to cover our financial damages by showing a compromising position.

It is unacceptable for you to pretend that you yourselves you are buying services from us. It is unacceptable for you to pretend that you yourselves are buying services from us.

I can assure you we will try to do our best to get our rightswhat we deserve/to get what we are owed. I can assure you we will try to do our best to get what we deserve/to get what we are owed.

It's not natural in English to say "get our rights" in this sentence. You could also adjust the end of the sentence to be more specific regarding what you are writing about.