Have you tried the unbent wire coat hanger thing to dislodge what is probably an accumulation of hair and soap? Our girls used to refer to the black slime which came out as “dead kittens”
There are some really cheap long flexible wire gadgets on the market for dragging up the gunge. The sort of thing you wish you’d got already when you have a problem.
In fact, I’m off to order one now, just in case. It’ll probably cost about £1.50 and take six weeks to get here from Beijing.
I'd be very cautious about trying to unblock it with a crochet hook or a straightened coat hanger. I tried it with a knitting needle and punctured the pipe underneath, causing a leak that penetrated through to the kitchen. Luckily I realised what I had done and quickly put the plug in and called the plumber who arrived surprisingly quickly.
The sink unblocker products work well. The bathroom ones dissolve hair and the kitchen ones work on grease. I have used the Mr Muscle one, which did the job. Good luck!
If you do the wire coat hanger thing (lucky you - yes I was one of the ones who said they enjoy it!) twist it around when it's down the plug hole and this catches more hair and gunge. Good Luck!