Dubious deal

I'm very disappointed with first for women insurance Policy. I have been with them for over a year now and decided to change my vehicle last month and buy a new one. I shopped around for quotes to cover my new vehicle and a few were giving me reasonable premium amounts. I then went to my insurance first for women and told them that I buying and new car and want a good premium, I also told them what their competitors were offer me. they said cause I'm a valued customer and they would like for me to stay they will give me a better quote of with gladly the did a stick to that. I chose to stay and was happy with the premium and no its a month with the new premium that I have been paying, today I receive a letter that my premium will change because the have under quoted me with the premium I'm paying and they have looked at other company and the value of vehicle I'm driving. after a month of being paying this now I'm being **** to and very angry with first for women how can they lie like this and only a month later when I have paid them decide to increase my premium. I'm so unhappy with first for women and I believe they lie to get and keep business for when it suits them.