The question is, what did you actually pay to the provider?
If you paid the provider $5000, and the provider issued you a refund of $200 (no matter what the reason was), then you only actually paid the provider $4800 and that is all you are allowed to claim as eligible expenses on your tax return.
If you originally submitted a reimbursement based on a receipt for $5000, there is no particular provision in the tax code that would allow you or require you to return the refunded amount to the FSA. You will end up reconciling this on your tax return. If you received $5000 reimbursement but only had $4800 of eligible expenses, then the other $200 will be added back to your taxable income. But, there is no additional penalty for the situation.