Frustrated

Completed the purchase and installation of a new Furnace and Air Conditioner. Pre-Paid total cost and learned on pre-install visit that the purchased items would not fit the intended location and to go with a smaller unit. Agreed to same and was advised that the smaller unit was about $4000.00 less and I would be credited the difference. Contacted the appropriate numbers to ascertain standing of my credit 1 month after installation and was advised that I would be credited the amount. 2 months later still no credit. Credit Dept Service is very poor and am still waiting