Service is poor

On 26/09/2017 Arthur came out to take measurements for a patio roof at my place, he was very professional and said that it would take 3 weeks for the roof to be installed after we made the payment of 50%, then on the 20th of October. After payment was done i phoned Arthur who then changed his story to 5 to 6 weeks waiting period... On Monday 20th I phoned their offices asking when they would be coming out to install the roof and they said coming Saturday. Today I phoned them again to confirm they changed the date again to 2nd of December. I am not sure why we have to wait forever but pay 50% immediately???? To me this is one of the most unprofessional companies i ever dealt with.