We acknowledge that, and tell them that we no longer feel welcome on campus (this will draw incoming), and that the last straw was charging for parking. If they ask for other examples, we give it to them (AthDept, no more College of Education, too many administrators taking meetings and not enough people doing actual work, loss of professors, professors with poor language and writing skills, etc.).
Since it's usually some student working the phones, we ask if the conversation is being recorded. If so, we tell them what a great job the caller has done, but, actions by the University have made us feel unwelcome, and if we're not welcome, our money isn't either. We also ask the caller to be sure to relay our response to their managers, or ask to speak to the managers themselves.
In one instance, the College of Engineering called and asked for another donation. We went through the above. We also asked the caller what the donation was to be used for? When the caller said she didn't know, she put on her supervisor. We again asked what the money would be used for, and the supervisor didn't know. The supervisor then said we could call the Dean to answer our questions. Our reply was, since the Dean had you call to ask for money, the Dean can call us. We also said we looked forward to hearing from him. We never did.
We are never rude or mean to the caller, who is usually a student. Not their fault for the ministrations of the "adults" over there. We are always kind to the caller, ask if they are a student, and if so, what they are studying. But, we always request that the caller convey our sentiments to higher ups.
And yet, we still get phone calls and solicitations via email, phone and snail mail. They are persistent.