Data usage

On 01 August 2022 I got my data allocation. 20GB anytime and 20GB Night owl. 05 August 2022 I am left with 8.35 GB. On the my vodacom app it shows that on 04 August 2022 I used 7.10 GB, and my router has been off all day on 05 August 2022 cause it wasn’t charged. I only switched sim cards with my router and handset after 18h00. Where did my data disappear to and what irritates me the most is that this isn’t the first time Vodacom does this. I was told I’d pay R149 for this deal but I’m always paying more than this and my allocation disappears for no apparent reason. This is nonsense.