Overflow problems

[Yorgi]

Good day am having an issue I hope someone can help with. Have a 150g tank that is plumbed to a bsmt sump. Exterior back over flow and we keep getting changes to water level in overflow box. Constantly have to adjust the stupid ball valve for drain on sump and it shouldn't happen. Seems to always happen when we need to top up water in sump. Any ideas? The place that did the install has no answers and has tried various solutions that way time cost me a pile but never solve this. They say it's our fault and someone is closing the valve but again we don't touch it until water level is dangerous high in overflow box. To me it seems like it constantly gets air locks but why? How do I solve this? Any experts that can come solve for me, ie: professionals? My service techs have no answers and am sick of paying for non solutions.
Any ideas are appreciated.