You are right to push back against the disappointment. When a Dutch person switches to English, it is usually a well-meaning attempt to help or speed things up, not a rejection of your Dutch skills. The key is to treat this as a normal part of the learning process and to have a calm, respectful strategy for continuing in Dutch.
First, understand why it happens. The Netherlands has very high English proficiency, and locals often switch automatically to make conversation easier for both sides. They may also be in a hurry or assume you prefer English. This is not a judgment on your accent or grammar. Recognizing this can prevent discouragement.
Your suggestion to keep responding in Dutch is excellent. To make this work smoothly, prepare a few polite phrases in advance. For example, you can say: "Ik wil graag Nederlands oefenen, vind je het goed?" (I want to practice Dutch, is that okay?) or "Sorry, mag ik het in Nederlands proberen?" (Sorry, may I try in Dutch?). Most people will appreciate your effort and switch back.
If they continue in English, you can still stick to Dutch. They might understand you perfectly even if they reply in English. This still gives you speaking practice and helps you build automaticity. Over time, as your Dutch improves, you will notice fewer switches.
Be honest with yourself about your level. If you are a beginner, start with simple interactions like ordering coffee or asking for directions. As you grow, move to more complex topics. Consistency matters more than perfection. Every conversation, even a short one in Dutch, is a win.
Also, consider the context. In busy tourist areas or during work hours, people may be less patient. In quieter neighborhoods or with older generations, you may get more encouragement to speak Dutch. Adjust your expectations accordingly.
Finally, do not take it personally. The switch is not a failure. It is a sign that you are trying, and that is what matters. Keep a journal of small victories, like a full sentence understood or a smile from a shopkeeper. Over time, these accumulate into real progress.
In short: prepare polite requests, stay consistent in using Dutch, and accept that some interactions will be bilingual. Your persistence will pay off, and you will gradually earn more opportunities to speak Dutch naturally.