Hey there!
We definitely understand that receiving a much higher bill than usual can be an unpleasant experienc. However, the charges are based on the usage you make. Have you had the chance to review your bills as @Cawtau suggested?
That said, I'll send you a private message shortly to look into it with you.
Hello again,
I understand that you might not have intended on making those calls. However, that doesn't mean that the charges are not valid. If the calls are on the system, they would have been made using your SIM card. What phone do you have? Is it a smartphone? It's possible that the phone has been infected with some sort of virus or malware. Charges for unknown calls is a rather common symptom of infected devices (see here).
If you do have a smartphone, you might consider running a virus and/or malware checker to see if your device has been infected. Unfortunately, some viruses/malware have been designed to fool anti-virus software. If antivirus and anti-malware app fail to remove viruses, it might be necessary to perform a factory reset of the device. However, even doing so might not remove all viruses (see here and here). It depends on what part of the device the virus was able to infect (see here). If they are able to identify the virus, there might be more effective means of removing it.
Even if you have an iPhone, they are not immune from the issue making random calls (see here, here, here, here, here, here, etc). It appears as though the issue is rather long-standing. That would be an Apple issue rather than a mobile provider issue. Yes, if the issue is not adddressed, it is entirely possible that they could happen again. Customers are responsible for the actions of their phones -- even if they weren't aware of its actions. It's not really possible to make calls on your account without your SIM. It's also rather unlikely that your SIM might have been cloned. In order to clone a SIM, they would need access to your SIM.
Mobile providers will just transmit what a customer's phone initiates. It the phone sends a text message, the provider will transmit that text message. If the phone makes a call, the provider will connect that call. The mobile providers cannot connect calls which were not initiated by a customers' phone. It is the customer's responsibility to ensure their devices are are not acting abnormally.
I'm sorry if this reply seems harsh. However, having a smartphone does not come without responsibilities. There are basic phones which can be used for emergencies and are not susceptible to OS glitches or viruses/malware.
Hope this helps 😀
Cheers
Hi Lamabazar! 
I hope your situation is resolved.
Have a nice day You can select me as best answer if you want 
Hello Lamabazar,
Welcome to the community!
Sorry to hear you've received that unexpectedly high bill amount. However, if the bills are from Fido, they are unlikely fake. That said, they may include additional charges incurred. Have you had a chance to view the billing details to see what the additional charges were actually for? You can view the details via My Account --> Billing & Payments. From there, you can Save and/or Print a PDF copy of your bill. Alternatively, you can also view the billing details online by selecting the required bill.
If you would like to discuss the matter further, you would need to contact customer service. In addition, they can also be contacted via Live Chat, Facebook, or Twitter. Those methods can be accessed via the contact page posted above.
Hope this helps 😀
Cheers
Hi lamabazar.
If you do not pay your bill, the bill will go to recovery agency to collect the funds, and your credit score at equifax and transunion will be very impacted. The best thing to do is to take an arrangment with Fido.
Have a nice day
