I absolutely would contact them regarding the design of the product and point out that this design is faulty, has caused pain etc.
How are they to know if they don't get any feedback?
I'd expect shapewear to be tightly fitting, I would not expect it to have plastic parts that cut in/dig in and leave marks that last many hours!
This week, I have objected to Boxt pissing me about (took four appointments, three cancellations by them/their contractor, to install) and got £150 back..
I am also complaining to the bed manufacturer that despite a 10 year guarantee, part of my bed frame has failed, and I've had to get it welded back together - I fully expect a partial refund from them too - their product was not fit for purpose, I have had to sleep on the floor for three nights and find a welder to fix it.
I hope that these complaints don't simply get me a bit of money back, but that they inform the companies involved so that they can do better in future!