I reckon the teacher might be right... but I can only guess from your description.
German schoolkids are usually taught that the /a/ in "cat" "sat" "mat" is pronounced "kätt". This is WRONG.
They learn that the /u/ found in "cut"/"butter"/"drug" is pronounced "katt" "batter" "dragg". This is WRONG.
The language used to sound slightly like this, but that was 5060 years ago, and things have changed.
So I am guessing you are coming from the traditional background and pronounce "thankyou" as "thÄnkju", "handy" as hÄndi, "manager" as the German "Mänätscher". That is why you find the teacher's pronunciation so wrong, and your ears would curl up at the edges to hear me talk. I encounter it all the time.
Actually we have discussed this topic frequently: try this link and scroll down a bit --
related discussionIn brief: the short English 'a' is NOT like German "ä", it is NOT a mixture of 'a' and 'e' (which is taught in German schools), it does NOT sound like the 'a' in German "Handy" which is pronounced [händi]. I speak for British English, but our US regular Peter Czukor is adamant that this is equally true for US English too.