Is it fair that work takes my shifts away?

Going to keep this short - might skip details.

I worked for this medical company on a full-time contract for over a year - left for my PGDE, stayed on zero hours. The company was expanding but didn't have enough HCAS, so they trained me on it and I worked weekends for them (£15 per hour). This inspired me to apply for graduate medicine too. I love it.

However, they are expanding more so and have hired contracted weekenders... therefore they get first choice. I am allocated shifts then told they have to give it to the contractors. It is seriously annoying. I am going to speak to my manager tomorrow about this because it's unfair for me and I am worried about losing my job. I asked for contracted weekends but received no reply. I TOTALLY get these people are contracted and I am not btw, but it's so disheartening seeing my name on schedule then removed - you can't give a shift then take it back over and over again because you made a mistake.

I am going to raise these points too:

- Did HCA and reception today - should get paid for both as doing two peoples' job. (Have done this a few times).

- Constantly being ignored - no reply to emails whatsoever.

- I asked to cover a site and he said no, then I saw another manager put someone else's name down (her sisters).

I am just worried they might ignore me and cut my hours. I also don't want to come across bratty. I only try to work two/three shifts a month, not even that much.