Has anyone ever written a paper and put your name on it?
Without knowing too many details of your situation, could you perhaps give the other author the benefit of the doubt? Cutting off all contact does seem harsh (unless you have other reasons) for what could simply be a misunderstanding.

I don't know the conventions of your field, but it seems in many science fields that authors are added if they contribute intellectual ideas on the research, not necessarily for doing the research. Other authors simply add support in some fashion, so get added. It is not uncommon to have many authors on a science paper. It does in fact get tricky because one can offend others by not including co-authors. 

I'm of the opinion that it's probably better to include someone who contributed in some fashion than not include them. You could argue that this dilutes research and is a "pure research game", but honestly, one paper is not going to make or break anyone's career.

Could this author simply have been trying to extend kindness, or perhaps thought you had a bigger role in the research than you actually felt you did?