I'm seeking other people who've had smart meter issues, to prove it's not just me and smart meters can be wrong and readings can glitch.

Lots of us, including me, have had (or are having) smart meter issues. Many, if not most, of these issues are due to a loss of comms so that the meters start acting as non-smart meters. Once the issue has been reported it is best to read the meters manually and submit readings at least monthly. If this isn't done then readings will be estimated, possibly for many months. When an actual reading (either smart, manual or meter reader) is finally submitted, a lot of reverse charges will probably show up on your bill refunding what was taken due to the estimated readings and charging for the actual consumption over the period of estimates. During this process, credit/debit balances can alter until the final correct balance is arrived at. Sometimes this final balance can be good news and sometimes not. It just depends on whether consumption was under-estimated or over-estimated over the period of the estimates.
I'm an Eon Next dual fuel customer with no particular expertise but have some time on my hands that I am using to try and help out a bit.