If your ad account has been disabled for violating Facebook Advertising Policies follow these steps to open a dispute use this appeal form to request investigation. Provide as full information as possible to prove that the advertising policies were not violated.

If you ad account was flagged for unusual activity, in most cases it is related to your payment method. 

"Your ads account has recently been flagged because of unusual activity. For security reasons, any ads you're running will be paused until you can confirm your account information by contacting Facebook."
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There are many reasons for this. Could be difference between account and billing name or they may think you're a fake person. It's faster to simply fill out the form, without digging too deep into the reasons.

Use this appeal form to request investigation.

Please also feel free to check out our blog post Essential Facebook ad policies to know for more insight on what you can advertise on Facebook.