You do not say what happened!
To fall below standard, you need to get defects taking your defect % above 2% which you can see on your seller dashboard.
What happened with the stolen items, if buyers opened cases then it is up to you deal with cases, and try to avoid defects.
Once below standard, and restrictions on selling, it is impossible to get back to above standard as you need a lot of sales, otherwise you have to wait 12 months for the defects to drop out of the calculation to get back to below 2%.
Reading your negative feedback, the first one you should have explained that ebay has not got a system to combine invoices, but any excess postage you would refund.
Next two, you could probably have got removed as ebay mentioned, but as I said above, you should have dealt with the sale, as getting ebay involved, just damages your account.
4th one, again buyer should have opened a NOT AS DESCRIBED CASE, damaged in post. If buyer had paid buyer protection fee, then ebay would have been responsible for making refund, not you, and no need for negative feedback.
