Verb conjugation of "stopfen" in German

As I have already mentioned in my last email, it is a breakthrough, I have never been so successful. I have visited several Spanish schools and would like to discuss that by telephone with you.
My correction were added and highlighted with yellow markers and attached to this email. Tell me now if you have any questions about grammar rules, since I was a teacher 10 years ago.
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.