Paper is based completely on my thesis, but I'm mentioned in the acknowledgements only, not as a co-author, what should I do? I developed a medical device for my master's project. The general idea was initiated by my supervisor but the rest of the work is mine (Design, build up, test, measurements, results and some additional functions I added to the idea).

After finishing the master thesis my supervisor started to write a paper about my project. The information in the paper comes from my master thesis and it merely rewrites and summarizes ideas from my thesis. Additionally, all the results and discussions were also picked from it. I was away during this because I found a job in a different city. My supervisor then started to contact me and asked me to give him feedback about what he wrote and to explain the results and said that he would name me as the co-author. I was supporting until the point that I got very busy, but soon his questions become orders and he started to ask very silly questions so I stopped responding.

Finally, he threatened to acknowledge my contribution only, that is, to only mention my name in the acknowledgement and not as a co-author, because he was not satisfied with my support / me not responding to his requests for help with the paper.

The whole paper is taken from my thesis and all the results are mine on top of the added support that I gave but finally, he'll mention me in the acknowledgements only. 

Is he right in doing this / allowed to do this and if not what can I do?

I am thinking of contacting the journal and explain all of this. What do you think?
I will try to give my perspective, on both sides if possible. In many countries, most incentive professors have for supervising undergraduate or MSc theses, is that some of them (or all if possible) may actually lead to a publication. There is a problem though: Most of the time undergraduate or MSc students leave the university and the paper usually can only be prepared after the student graduates. Unfortunately, at that time the student has already left academia and has really no interest in publishing, since he has more important things to do (like finding a job). This is quite the setting that the OP describes. 

Still in your case, your supervisor of the thesis has started writing the paper himself and he needs your help. Initially you provided the help needed but you became frustrated because it was more work than you wanted / expected to do, because (let's face it) the paper really does not make a huge difference to you. On the other hand, you want to stop him from publishing it solo. So, both parties are partially right to be angry at each other. You do not want to take orders from him and he does not want to be treated like an idiot (who calls his questions silly) from his former student. 

So, how can you fix this? For me, writing emails back and forth is not the way to discuss details for a paper. Why don't you use a better mean of communication such as skype, face-to-face meeting, phone call etc. You can there discuss all the details and your problem will be resolved. Of course he writes the paper and he will be the first author. But you get a publication and everyone is happy. And who knows? In the future you may collaborate further.