Upsetting incident

Why can't colleagues speak in a more considerate tone to me? I get into work, starting 2 hours earlier, as requested from my Manager 3 weeks ago. The moment I see my two colleagues, the first thing they say to me is "Why are you here at 10am?" One girl was like, there was an email sent last week, indicating that I was to start my shifts at 12pm this week. So, I told her, working 10 hour shifts this week, was pre-approved 3 weeks ago. That I tried emailing my Manager last week, asking if I'm still working the 10 hours shifts as mentioned earlier. Since I didn't get a reply from her, I decided to come in the usual time at 10am. Then, she's like, "Well, Manager can change her mind".. then, the other colleague asks me the same first question again.. then goes on saying, "We're fully staffed, you don't need to start earlier".. I explained to her, that 3 weeks ago, our Manager had me do 10 hour shifts for the rest of the month, as another colleague had to suddenly move to another position earlier than expected. Had me come earlier to help that person out with things during the sudden change.

I'm just feeling upset with how these two spoke to me. Having to start 2 hours earlier, benefits them, as I can start helping out with their tasks. Why are they making a big fuss about it? It's upsetting, and had become a negative start of my shift.

So, I messaged my Manager, saying I started at 10am today and asked if I'm continuing with these 10 hour shifts for the rest of the week, as mentioned 3 weeks ago. I also said I had emailed her this question last week too. So, until she tells me to disregard the schedule made 3 weeks ago, and go with the new updated schedule, I'm going to keep coming in at 10am. This 10 hour shift request, was made directly to me, so my other colleagues don't know about it. I just wish they could've worded their questions in a more considerate way. Not like they are interrogating and being annoyed as to why I'm at work earlier.