Regus review: Coworking desk continues to be charged after payment period terminates

I rent a coworking desk from Regus in Princes Street Edinburgh, UK. My contract period commenced in June. The duration is 15 months.
According to my agreement the cost for months 13/14/15 is waived. However, Regus has continued to charge my account beyond the period agreed. I contacted the Customer Care Specialist at the Account Helpdesk who was quick and helpful.

He replied: "In your particular situation, on the 30th of June you will receive the
invoice for the period of August: the monthly fee should be charged at
0.00 (and so on for the remaining months).

If by any chance the August monthly fee is not charged at 0.00, please
contact us via the help section of your online account and we will
immediately credit the charge."

Unfortunately Regus continues to send me urgent payment reminders, overdue notices and late payment charges. At the same time, no one from Regus is replying to my emails. This has been going on for three months. It's both stressful and a waste of my time. Regus is a massive company, I'm a freelancer and I feel completely outmatched. Please Help Me.