I would contact Emma Hardie Customer Service directly and explain everything including the other person that had the similar experience, with their M&S purchase.
If it were me in the email or call, I would definitely say that I had been looking forwards following many excellent reviews, and recommendations from friends regarding the balm, to trying it.
But this has definitely put you off, now leaving a rather bad taste regarding the brand, and doesn’t look like you will be converting over from your usual favourite.
In response if I were at Emma Hardie, I would certainly be offering a sincere apology, saying that the brand would take matters up with Marks & Spencers.
And to hopefully prove it’s not the usual standard of balm you should expect, at the very least offer you a free sample sized pot to convince you of such.
The bits should dissolve soon after the rest of the balm creating more of an oily palm. You certainly shouldn’t be feeling anything like uncomfortable, the bits should be cushioned within the rest of the balm and easily dissolve into the rest of the oily balm on your hands.