Screwed Access Cap in Garden After Installing new Sewage Treatment

[Bazrael]

I've recently had a new sewage treatment plant fitted, and along with the manhole cover and the vent for it, they left a screwed access cap (Floplast D292) sticking 3 inches above the lawn. It's about 3 feet away from the manhole cover where I presume they had to change the angle of the pipes underground.

I've tried to be careful when mowing, but managed to destroy it today.

Can anyone advise me whether there's a different form of cap I can replace it with that I might not destroy with a mower?

Thanks in advance,

Stuart