girl i was dating suddenly stopped replying

You probably should have spent a bit more time explaining the circumstances and seeing the lay of the land as it were before asking when you would see her. From her point of view you just started ignoring her and it's a really big assumption that you're still dating or anything after weeks of nothing. Considering she's had no other info to go on she has likely emotionally wrote you off and mentally moved on somewhat
I have to ask, if this was important to you surely you could have made contact some other way? contacted her online, through a friend, borrowed someone else's phone, even used a payphone? sent a letter? chapped their door? anything rather than doing literally nothing and leaving them to assume the worst for a month+
"Hi, it's XXX I got a new phone number so this is my new number and you can delete the old one" Like if that is literally what you sent her with no explanation at all that's pretty tone deaf. Think how many times she must have tried to call over weeks, sending texts like 'are you ok?' 'what's going on?' 'have I done something wrong'? 'why won't you talk to me?' etc. This will have put her through a lot and now a month on you've just strolled in all 'whassup I got a new number, when we hooking up?' like nothing happened?

You got ghosted. Simple and straight forward. If she wanted you she'd have messaged back. Don't waste more of your life and money on this.

True, you are right. I didn't think of that at the time - I just tried to play it "cool" but maybe I should have explained and added a little bit of small talk before inviting her out.
Do you think I could send another text now or would it come across as desperate?

Yes you absolutely should have explained immediately, along the lines of a grovelling apology.
I can't say I fancy your chances now tbh, it would be a massive hole to dig yourself out of. Even explaining now the whole stolen phone thing leaves her with all the same Q's I asked about why you didn't make any other effort to contact them.
I think you also need to ask yourself why you didn't make any other effort? Is this really a priority for you?

it was genuinely impossible for me to contact her sadly. I couldn't even contact my family or anyone. I don't have her on social media I only had her phone number and once my phone was taken I didn't have any other phone to use until I could save up to buy a new one. And logging into my social accounts on my computer was also impossible as it always needed a text verification code, I had to email my family haha.
I also got so screwed that I couldn't even buy any food as I was previously using apple pay and didn't have any physical cards or cash. My entire life came to a halt when that happened it was painful. She really was a priority just I messed up by not explaining when I text her, I just tried to play it cool.