Texts not sending abroad

[AC Question]

So I went to Poland (I'm from the UK) a few weeks ago - I'm on EE so my texts and calls abroad were included in my contract. When I first got there, I sent and received texts and calls fine, but one day my texts just stopped sending - like they sent in the morning but by late afternoon NO texts would send. I could still make calls, and receive texts, but texts wouldn't send. I just left it, went home, phone worked fine at home, but now I'm in Cambodia (using a different sim card) but texts are still not sending! I can make calls and receive texts still though, but I can't use mobile data or text - if I turn mobile data + roaming on, nothing happens. So I thought the phone might be locked, but the fact that I can make calls and could, for a few days, text is what is confusing me. Any ideas?!