Sprint Nextel Will not correct overage charge resulting from a faulty phone Internet

We have been Sprint/Nextel customers for seven plus years.  We have had the same plan, and consistent usage patterns for that whole period - in one two month period due to major life events we went over the allocated minutes - we paid those bills without comment or dispute.  

Several months ago we got a bill with more than 100 minutes over our usual time (we are usually about that much under.)  After several hours on the phone with Sprint - and three trips to the service center - they determined that our phones were malfunctioning - making calls on their own, and failing to hang up the call when we hung up -  and removed the overage charges and replaced the phones.  So far so good (except for the time and hassle it took to get it fixed.

Our last bill had a similar pattern of 1 minute calls one after the other - calls wouldn't go through on first several tries - and a number of very long calls - well outside the parameters of our normal usage.  I took my phone to the store - they confirmed that it was malfunctioning and replaced it.  Admittedly I was not as careful this time to tell them exactly what to look for and document - and they, according to the man on the phone tonight - did not do a thorough investigation.  As a result of that, and I suspect a policy that they cannot admit such mistakes, they offered to eliminate the overage ONLY if we switched to a higher rate plan - at 30$ a month more, it is just an installment plan on the disputed charges.  I was told that they took the overage charges off the prior time "as a courtesy" and would not do it again.  Really, since when is honest billing a "courtesy?"  If the phone, which they provide and for which we pay insurance, malfunctions, how is that my fault?

They are perfectly willing to bill for time that is clearly recorded in error.  We have been unhappy with the service for some time (calls that won't go through, incoming calls that don't ring through, failure to notify us of messages that are waiting for two days. Dropped calls etc.) After another multiple hour round of going through the standard "customer care" runaround script for over two hours we are done with this company.  And you should be too.

We will be changing phone companies ASAP.