So called to get my vehicle serviced and they told...

So called to get my vehicle serviced and they told me that it could only be serviced there only if I bought the vehicle there. I own a GMC and they told e to take it somewhere else. I have never heard of that I tried to talk to the service manager but he never seemed to be there at least that's what they told me. Funny thing is that I tool my vehicle there 3 weeks ago for a filter change. They have lost my business I will never go there again..AVOID!!!!