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These plants normally like neutral to alkaline, or a pH range of 6 to 8.

Campanula is an outdoor, full sun plant, so it can't thrive indoors. Using a campanula indoors is more like buying an especially long lasting flower bouquet. There's nothing wrong with that. You might like to try putting it outdoors, though - you can put it into a container with a few other plants if you don't have gardening space. Here's more information on these charmers: https://www.gardeningknowhow.com/ornamental/flowers/campanula/growing-campanula-bellflowers.htm
...and here's an article on plants that do flower well indoors: https://www.gardeningknowhow.com/houseplants/hpgen/good-indoor-plants-with-flowers-for-low-light.htm

The best way to promote blooms on a campanula bellflower is by deadheading. For more information on deadheading, please visit the following link:

https://www.gardeningknowhow.com/ornamental/flowers/fgen/deadheading-flowers.htm

Campanula can be deadheaded to encourage additional blooming, as most will continue blooming throughout June. If you've already been doing this and it's simply done flowering, go ahead and cut the plant back to encourage its new growth, along with a second wave of fall flowering.

Most likely an environmental issue. It's just not happy with the temperatures.
They will likely open on their own eventually.

https://www.gardeningknowhow.com/ornamental/flowers/campanula/growing-campanula-bellflowers.htm

You can deadhead the spent blooms. Here is more information: https://www.gardeningknowhow.com/ornamental/flowers/campanula/growing-campanula-bellflowers.htm