Subway complaint: Issues with manager regarding wages

I am a 22-year-old student who got into work via the manager call. I was asked to work the next day after the call. As a student, I was happy to work for the permitted time. But he asked me to work for 2 weeks as training which was not paid. I thought after the training things would be smooth but then I realized the workload was too much and I couldn’t handle work and studies, I was asked to work for more than my permitted hours I said no still the shift was put up. Due to the workload I was having severe back pain (sciatica). I asked them for a sick leave but I was denied due to staff shortage, the next day I called up the manager to say I was leaving the job because my class schedule was changed and the workload was more. By the time I worked there for 2 weeks which was 38 hours apart from training shifts. I asked him if it was ok, what should I do. He said it was alright and said I would get my minimum wage for the hours I worked by Dec 3rd. I waited until then and called him, he said he will not pay me the money I was supposed to work but I will only get 7 pounds which was way too much. The reason was that I didn’t give notice. But I mentioned to him that I was not going to work and asked him for his opinion. He paid me 266 for 38 hours after the argument. Later I realized he never mentioned anything about contracthow to leave a job the rules. I hereby claim that this is not a statement against a store subway but it is just against the manager Ahmed who is the area manager.