My rota’d hours got given to other people

I’ve been working as a waitress for about a month and a half. Most people that work at my restaurant have two jobs, but the manager knows I only have one. Despite this, I’ve only been getting like 8-12 hours a week but I put it down to being new. However, a lot of people started the same time as me, work another job and have been getting more shifts than me. This week, I was on the rota for 18 hours. With no explanation (wasn’t told by a manager, was told by experienced waitress who doesn’t speak much English so couldn’t ask her, not that she’d know anyway) I was told I wouldn’t be needed Friday or Saturday. This took my hours that week from 18 to 8. I was upset but put it down to them having overstaffed and cutting me because I was the least experienced. Just to find out when the new rota was put on the groupchat, other people had been given my shifts instead, including someone who started a week ago and has had 5 shifts that week.
I feel really undervalued and it’s making me think I’ve done something wrong or am bad at my job. I’m a little shy but have learnt most of what I need to know in terms of how things work and am always polite with customers. Looking at the rotas weekly, whether intentional or not, I seem to be singled out as getting the lowest hours despite being fully available and not having another job.
I texted my manager who hasn’t replied, conveniently. However I think it may have been the owner who changed the shifts, not her - either way, she always replies quick so I feel is ignoring me, and whoever changed the shifts, it’s not fair to give my shifts to people that have lots of hours that week already with no explanation leaving me working 8 hours :/

This isn’t the only issue at that job so obviously, I’m looking for jobs elsewhere. My problem is, until I find another job and can leave, I feel really anxious about going back as I feel under appreciated and like I’ve done something wrong, and also feel I don’t want to work for them when it suits them if they took my shifts away the week before?? Just wanted to vent, ask for advice and see if this has happened to anyone.

I’m nervous about asking my manager in person when she already has ignored my texts since as I mentioned, I’m shy, and don’t want to make it awkward if I have to work there till I find another job. Im aware it sounds like I’m doing a bad job but I really don’t think I’m doing that awfully to take shifts off me, I’m just very hurt and confused and stressed what to do.