This is happening in central Europe.
So basically I got this co-worker (let's call her Stacy) who regularly tries to undermine me. She disrupts my work, puts me in a bad light and doesn't cooperate with me at all.
Usually, she just talks about her products (in which I helped her a lot) as if she did them all alone and they were perfectly done. Which isn't the truth. She also puts all the "easy work" that she doesn't want to do on me and keeps all the bigger jobs, but at the same time complains that I don't help her enough (every time I'm done with one task I ask her for another one) and that she's way too overworked.
A few weeks ago, I had a meeting with my (our) boss to get a raise and receive overall feedback on how I am doing. He told me the amount of the raise 1 day beforehand. Just an hour before the official meeting, Stacy goes into the office of my boss and talks for half an hour with him. At the meeting with my boss he suddenly told me that my raise won't be possible and that he changed his mind. He told me Stacy was working really hard and was better than me. So my raise fell flat. (I sadly do not have evidence that Stacy talked to him about me in the discussion they had an hour before my meeting, but it is very logical (to me at least)).
Now Stacy is on vacation and blocked me out of her mail-access. I am the one who does her unfinished work when she's on vacation and the other way around. The jobs she left me are a complete mess, and I can't get any details because she blocked her mails getting through to me. My coworkers complain to me that these jobs aren't done yet and I'm still in the prep phase, because I need to collect every detail and make sense out of it. I texted Stacy over Whatsapp, she read the messages yesterday (ticks are blue) but didn't answer me. I'm furious and stressed out right now.
Should I report this to my boss/HR?
I don't know what details would help, so please comment them if you want some more.
EDIT: First of all thanks guys, your opinions helped a lot. For clarification, Stacy is not my boss, but we both have our own set of clients (4-5 clients pp). I'm not as long as Stacy in this company, so I don't have the real big jobs (except when Stacy is on vacation)
I will talk to my boss tomorrow anyway, so I will tackle this topic again. I collected as much evidence as I could and hope for the best.