locks you can't easily open yourself

Mistress told me to purchase a cock-cage, lock myself inside it after sending her a photo of the locked cage showing the combination code, followed by a second photo with the lock set randomly (with me in there). I wasn’t allowed to look at either the lock or the photos, which were then deleted. A few days later she would text me the correct combination.

It was slightly awkward; we’ll likely use a webcam for next time as this was just a trial run. The setup worked well for three days until the linking section of the cage snapped open, releasing me (not my fault! I wanted to obey Mistress). While playing with the lock afterwards, I discovered I could “pick” it by holding tension on the shackle while rotating the number wheels. There was a subtle shift in resistance when the correct wheel aligned. I knew cheap locks did this, but I was surprised that such good quality ones worked too.

So does anyone know of a brand for combination locks, and preferably a supplier link (UK preferred)? Being able to release yourself spoils that feeling of total reliance on Mistress somewhat. And before anyone says I shouldn’t need or want to try releasing myself: I am a Dom/switch, and being submissive is quite difficult.