Worse Customer Support Ever?

I am in the middle of what has become the most painful customer support experience I have ever had.  Despite purchasing a 3 year next day on-site warranty on a Precision 5510 My machine has now been broken for almost 1 month and repeated visits from technicians have only made the problem worse.

The first issue was a loose case which was separating slightly when I opened the screen.  It took almost 1 week for someone to show up to fix the issue after multiple missed appointments.  This technician tightened the case but broke the power connector, leaving me unable to charge my laptop.  Several calls to customer support and two weeks later (again after multiple appointments where the technician did not show up) and the new person "tries" to replace the motherboard.  In the process he breaks the new motherboard AND breaks my old motherboard attempting to put it back.  Now I have a laptop that will no longer boot and the Dell Service tech has just missed YET another appointment.  

I have spent over 10 hours on the phone with customer support who constantly make promises that a technician will arrive which doesn't happen.  I've been told by multiple people that the phone support has no way to contact the on-site person other then an email to a third-party dispatch company.  

Clearly if you have a machine that is critical purchasing the on-site warranty is worthless and you are better off saving the money and bringing it somewhere local if a problem occurs.  So far Dell has taken no steps to resolve this problem in any timely fashion and takes no responsibility for the quality of their onsite staff.  More then once I have heard from customer support that this work is contracted out to a third party and they have no control over them.  How can a company operate this way?