3 month guarantee on all repairs

I requested repairs on an aircon. They promise a 3 month guarantee. They did say with the first appointment that I need to replace a certain part. I paid the full amount for the service with the promise that they will get a price on the part for me the next day. I followed up numerous times - now the 3 month guarantee period is expiring, I still don't have a price and they do not answer my correspondence. And the original problem still exists.