Unwarranted interest rate increase

I have been with hsbc/gmcard since the early to mid 90's. My interest rate was a fixed 6.99%. A couple of weeks ago I received a notice that effective 12/9 my interest rate would be increased to 10.49%, an increase of 3.5% or 50% of my current rate. In attempting to speak with the retention department, I was told that the normal custmer service managers were able to do anything the retention department could do. In this case, since it was a decision affecting all the cardholders, my only choice is to opt out and close the account. Please note that there has never been any late payments or difficulty with this account and, even though they offered a skip pay program, in which a payment could be skipped with no penalty, other than interest, I only took advantage of this once, just two weeks prior prior to the rate increase notice. Seems like I was set up.