Is it possible to leave less than one star rating?...

Is it possible to leave less than one star rating?
I've had previous problems with HomeGround who took legal action against me for an unpaid bill they didn't tell me about. Even though they had my current address and up to date email, they used solicitors to track me to my previous addresses, it was only a matter of luck that I managed to receive the bill.
This time, I haven't been able to log in to there site to pay my ground rent, its taken 5 days to try and pay it and multiple card errors. I couldn't pay with any of my credit cards, eventually managed to pay with a debit card.
I would advise to avoid HomwGround, even if you find your prefect house, if HomeGround are the landlords, look elsewhere.
I haven't even mentioned the doubling of ground rent!!!