Billed for labour when system still under guarante

In September 2015, the control room informed me that there was a problem with my alarm- error messages received. The alarm system was installed in the last week of Jan 2015 by Enforce Electronics and had a 1 year guarantee. It was arranged for a technician to come check out my alarm on 30/09/2015. The technician found no fault. I then received a bill of R359 for an hour of labour. I felt that this was a ripoff for a system still under guarantee and that I should not have to pay. I queried my bill on a few occasions in October with the accounts dept.Tersia promised to give me feedback after checking with the technical dept. I am still waiting.