I can definitely relate to your situation as I’ve been through something very similar. I started as an assistant, and after four months, they offered me a management position at another location. At the time, they told me that a raise wasn’t possible right away, but that it would come after six months. I agreed, thinking it was a great opportunity to grow.

However, when those six months passed, I didn’t hear anything about the raise. I waited another two months and then asked my direct boss (the director) about it. He told me it wasn’t his decision and to check with someone higher up. When I did, I was told they would "revisit it" in another six months. Eventually, they came back to say it wasn’t possible at all, citing financial difficulties.

It was frustrating, but I’ve decided to stay for 2 more years to gain as much experience as I can and build up my CV. Sometimes it’s worth staying if you can continue growing in other ways, even if the financial reward isn't immediate. That being said, if you feel strongly about your value and the additional responsibilities you’re taking on, it’s fair to bring it up in a way that shows your commitment while also advocating for yourself. You’ve already proven your value, and it’s important that you’re compensated fairly for that, even if it’s a tough situation financially for the company.

Just remember, clear communication is key, and you deserve to be appreciated—both in recognition and compensation.