Walls – Reinforced concrete drilling: wall plug won’t fit

First-time driller here, so please bear with me! 🙂

I was trying to afix a shelf in the wall, and started to drill the holes for its mounting brackets. The wall is reinforced concrete, and I was using a standard 6mm masonry drill bit attached to a hammer-function-enabled machine. I stumbled upon several problems:

1) The drill bit at some point became fixed in the wall and was no longer spinning – only the machine's circular grip was spinning around it. I tightened the grip and continued, but this happened several times.

2) The drill would still not advance, so I ended up using a 4mm bit to go in first, and then followed up with the 6mm one that I needed.

3) Although I used a wall detector to check for pipes/wires before drilling, I was very nervous since the detector seemed to very unreliably beep over the same locations, perhaps because of the metalic reinforcing bars in the concrete. In the absence of (useful) building plans, is there any other way to prevent drilling into pipes or wires?

4) After finishing drilling with the 6mm bit, my wall plug (anchor) did not fit the hole, even when (gently) hammered in; and drilling some more (by applying pressure towards the sides of the hole) to make it a bit wider also did not suffice. Both of these strategies together (hammer+enlarging the hole with same drill bit) had previously worked when I drilled into a softer wall (not sure if that was cellular concrete or drywall)!

5) I reckoned that given the hardness of concrete, I maybe just need to use the next-larger drill bit size, 7mm, to fit the 6mm plug; but my set does not include one (the next up is 8mm), and none of the sets I can see on Amazon include 7mm (for concrete or masonry) either, only for wood!

Sorry for the long and rather incoherent question, but I hope that someone can advise on how to best proceed despite my beginner mistakes!