I haven't been promoted since I started inat this company two years ago, I'm in a terrible rut!

Should I pay now or can I run up the bills and pay later?

This sentence makes sense, but I think it sounds a little sarcastic! Running up debt isn't something you'd do intentionally, so when you acknowledge it as an option here it feels like you're making a subtle joke.

When I signed the contract I did not know what I amwas letting myself in for – it turned out to be a really horrible role.

Because the rest of the sentence is in past tense!