Judith: If you are still working then they won't go back to "normal." Normal is when you have no income at all which impacts your monthly benefit. The maximum SSI benefit is $733 a month. We have no idea what your "normal" is.
There is a general $20 a month exclusion which applies only once and it can be applied to either earned income or unearned income.
If you have unearned income, SSI counts all but $20. So if you have a social security benefit of $500, SSI counts $480 of it and reduces the SSI benefit by $480.
If you have earned income, SSI counts half of what you earn over $65 ($85 if the general exclusion isn't applied to any other income). So if you earned $500-$65=$435. Half of $435=$217.50. The SSI benefit is reduced by $217 two months later. If you earn it in December it reduces the February benefit.
Income is counted when received unless it is earned income.
When there is a discrepancy it must be resolved by contacting the employer for proof. How long that takes depends upon how quickly the employer fills out the form. Once received, how long it takes to input depends upon how much work the claims rep has and how much time, after interviewing, they have to spend on their workload.
The cut IS normal. They caught the error and fixed it. In fact, if they overpaid you for some time, then you could be getting less than normal and when you have paid back what you owe, then they would pay you more but don't expect them to pay you the over-inflated erroneous amount.
If you contact them with evidence of your income (pay slips, bank statements) etc. then the chances are good.
If you do nothing and just hope they'll spot the error themselves – the chances are poor.
It would be a long process if you can get them to understand what happend, your better off just keeping it what you have unless your getting jiped a lot, it's a hassle