@brenda, as @anon23935806 also said, I can highly recommend moving to a rolling 30 day contract over being with GiffGaff. Nothing against GiffGaff, they provide great flexibility when first starting out, but do nothing to help show consistent payments.
I’m currently on a rolling 30 day with Plusnet. It was 4GB of data for £10 a month. They then had a new offer for 5GB for the same price, so I rang them up and from the following month I was on the newer deal, no problem as it is only a 30 day commitment. However, it is taken by DD and still counts as a contract, so you get those benefits. (and since it comes out of my Monzo account I see it 3 days before as an upcoming payment 
)
MSE has a page where it shows latest offers, and you can get your PAC code fro GiffGaff so your number transfers across.
https://www.moneysavingexpert.com/phones/cheap-sim-only-contracts/
Could also bump the thread on here about SIM only plans: https://community.monzo.com/t/sim-only-plans-what-do-you-guys-think/37084/28
And here: https://community.monzo.com/t/share-your-money-saving-tips/35989
r/ULPersonalFinance has a FAQ page on LISA’s its worth reading: https://www.reddit.com/r/UKPersonalFinance/wiki/lisa
And a flowchart,
https://community.monzo.com/t/r-ukpersonalfinance-updated-flowchart/23587?u=rolanddeschain