For the meal plan you'd really need to check the terms of it:
https://www.birmingham.ac.uk/accommodation/our-services/student-living-plus.aspxSounds like they do rollover each week up until the end of term, but it doesn't accrue between terms. I suspect the reason for the price difference is because in reality the food costs on campus are rather more than the equivalent where you aren't a captive audience, and possibly an assumption most students will end up with credit wasted at the end of term? I can't really imagine students routinely eating £64 a week of food and drink...unless it can be used at Waitrose or something!
Based on the accommodation website it looks like the student living plus option is £50 per week more which is most of that value of the student living plus. You get maybe £15 "extra" value out of it in theory, but in practice you could save much more on groceries buying your own meals if you're sensible with your shopping. Like I said, you can certainly live off £25-35 a week as a student reasonably I think.
If you've already paid a deposit you would lose that if you opt out. If you're confident between your family supporting you and in seeking a part-time job though then by all means stick with it. I don't think it's the best option but it may be more costly reversing it at this stage potentially.
Also I think framing things in terms of "better" or "good" accommodation even might be a bit off base - in general from what I've seen and experience, student accommodation tends to be largely similar and kind of similar shades of crap
I would honestly just go for the cheapest option which won't make you go crazy in your room and grind it out while making the most of other activities!
While I can understand for example some unis offer much cheaper rooms but that are shared
rooms rather than shared flats and that isn't for everyone, I think things like ensuites and catered accommodation/meal plans tend to be money traps for new students, personally. Yes it's a bit of an adjustment getting used to planning your own meals, buying your own food, and respecting other people's boundaries (and hoping they respect yours!) with shared bathrooms with strangers, but that's part of the experience of growing up and going to uni, I think
These latter points are more for posterity for others who may see this, as it may not be feasible for you to change things now as noted.