Wrong phone credit used

[#1]

I have received multiple email saying I have used up my home phone credit limit and now its reached limit. I don't even have a phone plugged in to my socket, I only use the wifi. I have checked the calls in my account and I dont know any of them. Then I called the customer service about the situation and they just respond that they have checked and somebody is using the phoneline. But NO ONE in my house is using phone line, and again, I dont even have a phone. But the customer service doest solve the problem at all. Now I am so confused.
Can anyone please help?

[#2]

Do all the phone numbers consist of low digits I.e 1,2,3 ? 

[#3]

No, there are many numbers called and they consist of digit from 0-9.

[#4]

@FL 

Do have (or can you borrow) a phone to plug in and check that your line has not been inadvertently swapped with another one at the cabinet, such that the other persons calls are being charged to your telephone account.

Plug a phone in, dial 17070, then listen to the number which will be read out and check that it's correct.

[#5]

Is there anything else connected to the phone line , e.g sky box , alarm system ?

If not then it may be a crossed line , try dialling 17070 and see if it reports your correct  phone number

Other than that , raise a phone fault https://www.plus.net/help/report-a-problem/phone/

[#6]

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@FL wrote:
No, there are many numbers called and they consist of digit from 0-9.

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Are they to various area codes, or all to your local area code?

[#7]

They are to various area codes, including my area code

[#8]

OK, then @MisterW 's advice is the way to go.

[#9]

Hi @FL,

I'm very sorry to hear about the recent experience. I can see that since this thread was started, an engineer appointment has been booked to investigate the possibility of a crossed line. Should any issues persist after the visit's taken place, please let us know and we will be more than happy to continue the investigation.