Got offered the job I applied for, been trained up for a complete different position

I applied for a security job with a security company a few months back and they were offering more money and more hours.
I had two interviews, one with the security company themselves and another interview with the client.
In the client interview I was told that I would be covering the lady who is front of house(receptionist) while she is on maternity leave, the interviewer said this position "pays more" but never disclosed the actually rate.
I agreed as I have front of house experience so it wouldn't be new to me.
On Monday last I started my front of house/security training, I.e, getting the hang of the new systems and familiarising myself with the building etc...
All was going well, really well, too well if you ask me, something told me this is too good to be true but I went along with it.
I asked the lady who I'll be covering while on maternity leave if she wouldnt mind telling me what her rate of pay is as I haven't had confirmation, she told me 14.50ph.
I then emailed the girl who I had the interview with in the security company about my rate of pay, She said my rate is 11.35 + 1.50 site allowance. 13.85 altogether.
Surely this isn't right ? So I went to the supervisor and asked about this, he basically said keep mouth shut and leave it for a few months, which I didn't appreciate.

Moral of the story:

Applied for a security position (48hrs PW @12.50ph)

Get accepted but put into a complete different position (40hrs PW @ 12.85ph)

The lady going on maternity leave is moving from Dublin to mayo as it cheaper to rent and everyone reckons she wont be returning after her maternity leave so this is looking like a permanent position. (She's getting 40hrs @ 14.50Ph)

Getting paid less than the lady who is going on maternity and told to keep my mouth shut.

I've added it up and I'm making an extra 4 euro a week but I have to travel further so I'm really loosing money and doing 10times the amount of work I was doing in my previously job as I'm basically a PA/receptionist to the client

In the interview I was told the front of house "pays more".
From my understanding the meaning of "pays more" is an extra few euro, not 35cent. (Security Job was advertised for 12.50ph)

I feel like I was mislead and taken advantage of.

Do I have a leg to stand on ?
Will I get fired if I refuse to do the job for anything less than 14.50 ?
I haven't signed a contract yet.

TIA!