BAD SERVICE FROM INTERNET PROVIDER

I have had nothing but trouble from this internet provider. I have a tenant in 213 The Epic, Patricia Road, Atholl, Sandton. My tenant has not had internet connection for over 6 weeks. It has become so bad that the tenant has only given me half of the rent, and is threatening to stop paying altogether. I have written letters, spoken to the supplier and all to no avail. I would like my client to be satisfied, and aat the same time I will then be paid the usual rental.