Generally speaking, it is your responsibility to make yourself understood. As a non-native, you do have a harder job than a native.
It is legitimate for your colleagues to comment on your accent if they don't understand you. If they're mocking you or disparaging you, it's definitely inappropriate. However, there is a good chance that they simply don't understand you. Keep in mind that different people will have had different exposure to accents like yours. Just because a majority understands you doesn't imply that everybody understands you.
Different languages have different pitch ranges, and the ear (or rather a part of the brain that interprets signals from the ear) is to some extent trained to focus on certain ranges. The people who don't understand you might be less sensitive in your range. This can be compounded by them being slightly hard-of-hearing, in a way that doesn't impact their comprehension of most natives but that hinders their comprehension of your accent. If that's the case, they may not even be aware of it — and if they are then it's often a sensitive subject, because it's a sign of age (which by the way could explain why more senior colleagues have more trouble understanding you).
You may need to articulate more or speak slower. On their part, they may need to pay more attention, to devote some conscious brain processing that they wouldn't need when listening to natives. The level of background noise can also be an issue (for instance, I find it harder to understand English against a noisy background than my native language, even when I'd understand the same people perfectly in a quiet environment).
If they repeat words back at you, it may be to confirm what you said, in which case you should acknowledge (orally or by nodding). They may also do this because you mispronounced a word and they're letting you know how to say it correctly. It could even be a combination of both if they're not sure how you'd take corrections. Do clarify with them whether you want to be corrected when you make a mistake; if you chose to live in a country where you don't speak the language natively, there's generally a presumption that you want to learn and improve, but it's best if you clarify your wishes with your colleagues.
Conversely, if you have trouble understanding your colleagues, do tell them. It's their responsibility to make themselves understood too. Depending on your level in the native language, you may or may not expect to understand everything, but make sure at least to let your colleagues know when you understand and when you don't, and do ask them to speak more distinctly or louder if necessary, or to seek environments with less background noise.