Hi Alexander,
I'm sorry to hear about the issues you have your calculators! I bought mine a couple of years ago and it still works perfectly (and it still get's used quite a bit...)
In this forum we usually discuss analog ICs from TI - so I'm not sure how many people from our calculator team are actually following the posts in this forum. But there is a website with contacts for the "Education Technology" part of Texas Instruments. I would suggest calling them or writing an email about your issue.
http://education.ti.com/educationportal/sites/US/nonProductSingle/support_contact.html
Hope this helps.
Thomas
