I started work in the beginning of this year as a volunteer in a charity. I was working for a manager in the office and I was originally hired to help him on a project that he was working on. When I first came into the office some of the other co-workers stated asking me to do some of their work for them because someone told them I had creative writing skills. I was okay with it, however, my boss sort of came up behind me while I was helping them with some of their stuff and he said that he didn't want me doing other people's work for them. He spoke to one of them and told them not to hand over any work to me anymore and that I was only supposed to work on whatever projects he handed over to me.
How ever, I became quite friendly with someone else whom I will call Lady XYZ and would occasionally help her with things if I had time to. Last week Friday, (my manager had traveled for a few days) she asked me to do her a favor, which was helping her with some part of the post. I did this. The next week, she asked me again if I could help with the post, while she was away from the office for the next few days and I said no because I remembered what my boss had told me. I asked her who was going to do the post when she left .She said she didn't know and that it wasn't her job to figure it out. That it was HR's job to make sure the post is done. She also said she didn't know how she ended up doing the post, that shes tried to tell HR to create a rota of people to do the post so its not just one person doing it as well as having their own workload to do but for the past one year she has mostly been the only one doing the post which was not her job in the first place. She also said that the HR manager doesn't have an assistant so she tries to offload it on whoever she can basically. A day after the HR manager comes up to me, and says "I understand Lady XYZ trained you to do the post" and dumps it on my table and walks off. I explained to her that I already told Lady XYZ that I wasn't doing the post but she was just like, "well you've been trained to do it, so ..." So I did it that day.
Today again she came back and asked me to do the post, and I was working on something my manager had asked me to do while he was away and I said I couldn't and that I was working on something. She dumped it on my table again and said its not optional and then she leaves . The manner of her doing it was very rude, and also, I don't know how doing someone a favor translates to something that I'm now expected to do everyday.
I spoke to her again afterwards and she then said she felt I was only busy when I wanted to be because she claims that she sees me walking around chatting to people in the office . I told her that I only go to ask people things which I genuinely need to know and unfortunately I've been told in the past that I just come to work , do my work and go home and I was getting a lot of attitude for that because others felt I wasn't friendly. I didn't want them to think that so I started trying to be more friendly with colleagues so when I need to ask someone something I try to make conversation with them so they don't feel that I only talk to them when I want something. Unfortunately this seems to have backfired because the HR manager then assumed that since I was being friendly and helpful that I didn't have any work to do , so when she brought me the post and I said no , she assumed that I simply wasn't doing it because I just didn't want to. Which to me doesn't make any sense because I genuinely do have work to do . Shes not the one in charge of my workload, so I'm curious as to how and why she would assume that I wasn't doing anything.
I feel slightly uncomfortable with this situation as it seems that me trying to be helpful is being taken for granted. At the same time I understand that it is a business and we are all required to pitch in from time to time which I am very willing to do. Which is why I helped in the first place. At the same time I don't know if maybe I am in the wrong, for firstly taking on co-workers duties when I was already told not to (the answer to that is probably yes, but I simply didn't know how to say my manager told me not to do XYZ without them thinking I was just being lazy/ uncooperative/ teamworker) or if I'm wrong for saying that I was genuinely working on something and so I couldn't do it.
In either case, what should I do now?