SMETS 1 meters are being transferred onto the DCC network from standalone supplier networks. When completed (end of 2022) they will in most respects have the same functionality as SMETS2. Many have already been migrated and functionality restored, but customers still waiting have no way of knowing when or even if their meter can be resurrected. Come the end of 2022 we will probably learn more.
But if your meters are SMETS 2 E.On Next should be capable of getting them to work properly. Try the Citizens Advice smart meter checker and report back. If E.On Next can't get them working they'll need to replace some or all of your kit. Give them a new call, tell them they have a couple of weeks to sort it out, then make a complaint if no fix is forthcoming.
Unfortunately, there are no financial drawbacks for suppliers in having customers with non-functioning smart meter systems - if there were they'd fix them quicker. There are of course financial incentives to install the things in the first place - but nothing to keep them working at all.