The Federal Trade Commission will refund more than $88 million to more than 2.7 million AT&T Inc. customers as part of a case into mobile cramming.

The agency said Dec. 8 that it will refund the affected customers through bill credits within the next 75 days, while more than 300,000 former customers will receive a check. The average refund amount is $31.

In 2014, AT&T unit AT&T Mobility LLC agreed to enter into a $105 million settlement to resolve an inquiry involving the FTC, the FCC and the attorneys general of all 50 states and the District of Columbia investigating allegations of unauthorized third-party charges billed to AT&T wireless customers.

Regulators alleged that the carrier engaged in a practice known as mobile cramming, billing customers for charges originated by other companies, usually in amounts of $9.99 per month, for content such as ringtones, wallpapers or entertainment news.

The FTC further claimed that the company retained nearly 35% of the charges imposed on customers.