Reducing work hours?

[Hobnob_Goblin]

Hello, clueless new starter here. I'm seeking advice on how to go about reducing my working hours.

First a bit of context:

I'm halfway into a 4-week flexi contract with Tesco as a picker. I'm contracted at 20 hours but this past week I've done 40.

I have some underlying health problems that I'm still trying to get diagnosed, but I can't afford to get a job elsewhere. It's relatively easy to hide and it doesn't impact my ability to work too greatly. My joints are in agony during and after long shifts, and working 5 days a week isn't giving me much time for my body to recover properly. 

I'm assuming that my induction day was supposed to inform me about what I could and could not do on a Flexi contract...there was barely any information on the matter and I was stupid and forgot to ask about how overtime worked. From what I've heard you can be sacked for refusing to work overtime, but I don't know how true that is.

I've found that communication in my branch is pretty bad so far. It's incredibly difficult to get a hold of any supervisors/managers and when you finally do they don't give you their full attention for longer than 10 seconds. I've been trying to ask to work 4 days instead of 5. The person who I spoke to said she'd put it down on a post-it note for the manager, but I've got my rota back and my request was ignored, the next 2 weeks are also 40 hours.

I'm afraid to tell the higher-ups that I'm struggling with pain from working more than I'm physically capable of in fear of being let go of at the end of my current contract. I'd ideally like to keep the job for at least a few months since it's very difficult to find somewhere that doesn't have the age pay rate difference.

Does anyone have any advice on how to approach this situation? I'd like to keep both my job and all four of my limbs.

[Redshoes]

It's all on your availability. You can just cap the hours, or days. You have to show a minimum of nine hours availability above your contracted hours. If on old system it's just nine hours. If heading towards work and pay its nine hours spread over five days but can only be either before or after contracted hours but not both, you need to have two clear days off and can't show anything other than contracted hours on Sunday's.
Just ask to update your availability due to a change in personal circumstances and cap the amount of hours you can work in a week. 
Just be aware that as a new start and on a temp contract if you restrict too much you may not be kept on. Your health comes first though so if you are finding that you really can't do the job you need to have that conversation. Your manager needs to know, there might be a more suitable job for you in the store. We don't really have much in the way of light duty jobs but it might be worth asking.

[lucgeo]

Do you have contracted days? How many?

The days you work, should be your contracted days...so depending on your pay system for store, be it the old system of nine hours extra fulfilment requirement, or the new system of nine hours EITHER before or after your contracted shifts. Therefore these 40 hours rota you are being presented with are against policy.
Add to which, you should be ASKED if you are available to do extra overtime, with an acceptable notice period of four weeks in advance. They will tell you it's 24 hours...that is emergency only, so they can't keep saying 24 hours notice...ask what the emergency is this time
If your manager is ignoring you, request, in writing, a " let's talk" to discuss the overload of hours.
Did you divulge your underlying health problems at your induction?

As a newbie you are being exploited. You can only be sacked, (non fulfilment of contract) if you continuously refuse to do any extra than your contracted core 20 hours.

Also with the new lockdown, some staff going off shielding, going into isolation or, God forbid, contracting the virus, it certainly wouldn't be good management to dispense with the trained staff they already have in place