They increase prices when ever they want to

Ntp security in pta west increase prices when ever they fill like it .I took a contract with them late last year saying i will pay R180 for the first 12 month and prices will increase after 12 month to be R235 . beginning of April they have send us latter saying prices will increase end of April to be R202 . I fill like am being ********** and am not happy about they services .