5 months later, no products received and they want us to pay.

My Fiancé accepted an offer via telephone for a data top up on her current number from Mondo in August of this year. It is now the 23rd of December and she's not yet received anything. We canceled her debit order in November as nothing was received by my Fiancé. We phoned mondo and they told us that the top up has been issued and has been used. We asked for a statement as she also didn't receive one. They told us that a statement has been sent. When we asked to where they gave us an email address that she doesn't own, a Number she doesn't own and the address doesn't exist. However the number being allocated with data is one digit different from a number we do recognize. We reported the issues and was told that we would be contacted in 48h, which they never did. We're now being threatened with credit boroughs and that her services will stop working and such. A constant sms has and is being sent to us telling us that we need to pay for something we never received, of which all of her information was incorrectly received and nothing has been done to rectify our situation. It's been an absolute nightmare to sort out this situation with them and to date we've not been contacted with a resolution but rather threats. We're at the point of seeking legal advice because of this.