Please help identify cat parasite

My 12 year old tabby cat has a strange lump on her back. I thought it was a tick at first, but after looking at pictures on the internet I'm not so sure. I felt the lump while stroking her, then had a closer look. I couldn't see anything at first, and was trying to part her hair when a lump of it fell off. This left a small bald patch, with a black lump attached. It's thin and standing proud, about 5 mm long.
So kinda like () with the narrow end attached to her flesh, very much black rather than brown tick colour
.
Please help! I'm very worried.

It could conceivable be a bot fly. A vet should definitely see it; trying to remove one can make a cat very sick.

If there was a visible hole a few millimeters across it would have been botfly larvae, but what you described sounds more like a tick. They ain't all the same colour and some are very small even bloated.