Want to switch SIM cards on 2 phones does rollover data I save come upgrade sim

[Chipchipaway]

I have two SIM cards on 2mb £8 per month. If I move to the 3mb for £6 per month. I have 74mbs on rollover, when I switch will that also transfers over to the new sims please?

[caesarome]

Any saved data remains on the device so long as you add the new data package to

the same sim so you don't order a new sim.

Any saved data in your piggybank is safe come what May as you would only lose this if you cancelled both sims that you have,

[PandJ2020]

Yes, you can change your mix once a month - it does not impact your saved data in the piggybank.  As noted, this is only lost when the last SIM on the account is cancelled.