Got fired from my retail job in England after 6 years for sickness when i had a sick note

Hi i recently got fired from my retail job in a supermarket for my sickness/attendance. In retail if you have 3 sicknesses or more than 3% of your contracted hours you get a mandatory disciplinary/investigation. On the 1st of Jan i was really ill (i had food poisoning but i didn't know at this point) so i called in sick which they asked if i had alcohol the night before which i had but it wasn't enough to get me drunk and certainly didn't go out which i told them in my investigation. I went back for a few shifts since i was fearing getting a disciplinary for being off. I had multiple staff notice me feeling extremely ill recommending i get paracetemol and to sit down and even a manager asking for me to go home which i told him i couldn't or i would get a disciplinary. It got bad enough that i was literally Pooping blood every 10 mins. I finally called 911 and they referred me to my gp that asked for a stool sample. Stool sample came back with confirmation of campylobacter aka food poisoning. I handed in my doctors note which gave me a week off. I came back to work to find i had 2 different disciplinaries/investigations since they said i worked a few shifts and treated it as separate sicknesses. 1st manager was somewhat understanding and only gave me a 1st written warning and took it no further. 2nd disciplinary the manager was guilt tripping me for being sick and spinning my words and making it seem like i was on a hangover even though i had my doctors note in front of me. They told me that food poisoning doesn't go on for that long since my manager had it her self (because my manager thinks she some qualified doctor or something). I told them couldn't they get in legal trouble for firing me with a sick note. They said that since my note didn't cover the start of my illness they were fine and laughed at me. I might've shot myself in the foot because they asked if i cared that they were short staffed because i was ill and i ended up saying "i don't give a shit i had the worst month". They then came back to me to say i was dismissed but have 5 weeks notice period which i ended up walking out of since i was so angry. I also had holiday booked for the next weekend which they took off without notice and then rang me up to ask where i was (i just got paid and they didn't pay my holiday). Also they didn't pay my sick pay for all this so for 2 months i've lost several hundred pounds when i'm already minimum wage. I even asked work for SSP help which they said they would then ignored me.

Since i now have to rely on UC it doesn't cover my rent and i have absolutely no money left and i'm now having to resort to selling my stuff to get by all because i was extremely sick.

Sorry for the yap fest, anyways i was wondering what options i have here and if they are correct in saying that i have no legal ground since my doctors note only covers that last week of my sickness?