Thriller/mystery where the main character gets abducted

[Iqra]

I read this book around 5+ years ago,
The main character is a female who gets trapped in an apartment and her captor is a man who essentially is slowly poisoning her,so throughout the book she is carrying out activities he forces her to do and as a result she gets sicker and sicker until she finally stabs him and hangs a banner on the balcony that says HELP (drawn with his blood)
In the book he gives her a tattoo,gives her drinks containing the poison,gives her gifts where the wrapping is covered in crystal poison and more.
Apologies if this description is very vague,I can only remember certain parts from the book

[Iqra]

I remember at the beginning of the book she is in the car with the man who ends up trapping her and she pretends to text her family and let them know where she is

[Lobstergirl, au gratin]

Your header is too vague - you must add plot details to it. We close threads with vague headers !