Ofcom said both companies broke consumer protection rules by failing to make clear the charges customers would have to pay if they ended their contract early and levying “excessive” fees to leave.
The watchdog’s investigation into early-exit charges found around 400,000 EE customers who ended their contracts early were over-billed, which saw customers overpaying up to £4.3 million.
It added that almost 82,000 Virgin Media customers were overcharged a total of just under £2.8 million.
As a result, Ofcom has fined BT-owned EE £6.3 million and Liberty Global’s Virgin Media £7 million.
Phone and broadband companies can charge customers who decide to leave their contracts early, but under Ofcom rules, those charges must be made clear to customers, and must not make switching to another provider too costly.
Gaucho Rasmussen, Ofcom’s director of investigations and enforcement, said: “EE and Virgin Media broke our rules by overcharging people who ended their contracts early.
“Those people were left out of pocket, and the charges amounted to millions of pounds. That is unacceptable.”
He added the fines “send a clear message to all phone and broadband firms that they must play by the rules”.
Both companies have since agreed to change their terms and reduce exit charges, Ofcom said.
Virgin Media has vowed to appeal against Ofcom’s decision.
Tom Mockridge, chief executive of Virgin Media, said: “We profoundly disagree with Ofcom’s ruling. This decision and fine is not justified, proportionate or reasonable.
“A small percentage of customers were charged an incorrect amount when they ended one or more of their services early and for that we are very sorry.
“As soon as we became aware of the mistake we apologised and took swift action to put it right by paying refunds, with interest, to everyone affected.
“For those few people we could not locate, we have made an equivalent donation to charity.”