bank increased my mortgage interest rate by 0.75% for no solid reasons

[Jitao Niu]

A local bank suddenly increased the rates of several loans, resulting in over $40,000 increase of interest annually.

when I found out, I asked for the reason. They said it's because I did not follow the rules for marinating operation and deposits accounts at the bank. In fact, I deposited all the rent to the bank and only paid the mortgage from the account, leaving large amount in balance in checking accounts in about two years. The bank have been  ignoring my emails and calls. 

Not sure what to do now. Wonder if anyone had similar issues?