What do I do? my work contract has changed

I (f24) already have had some concerns over a notice period for my new job. It’s a legal secretary role paying £22,200. At first I was concerned because the contract stated that the notice period I would have to give to quit would be 3 months. For me to get terminated, the firm can fire me within a week during the first three months and then after they can in 1 month. I initially felt frustrated but just decided in the end to go along because I wanted a job. However today I feel really frustrated. I had signed my contract. Then my line manager told me my contract would have to be amended because it has the wrong hours on it. I thought this would be fine. However without telling me they also increased the notice period to 4 months instead. I’m frustrated by this and feel like it’s kind of taking the piss. I’d understand if it was a managerial role but for a minimum wage secretary? I don’t know how to approach this. I haven’t signed it. But I’m wondering how others would handle this situation