Cramming happens when minor expenses are added to an invoice by a third party without the agreement or authorization of the subscriber. Usually cramming is connected and practiced by phone companies and third parties connected to these companies. Cramming is a type of phone scam.
You can be charged for many types of services that will appear on your bill. In addition to billing for its own services, your company may bill you on behalf of other companies for services this different company sells.

In cramming, a company may create a single charge or monthly subscription for potentially millions of people, charging for nothing. Often, these charges go unnoticed because when you pay them they are on your regular monthly bill even though you don’t understand why they are there.
Tips To Avoid Cramming

If you are certain that the company that is charging you is not honest and your bills are crammed, immediately cancel your service with that company and search for a better company with no cramming practices. Even after you canceled your subscription check your bank or credit card statements for any further charges.
Fortunately “slamming” and “cramming” customers are is banned in many countries worldwise. Therefor if you spot this practiced on your bills, you can report this to your authorities and to any other consumer protection organizations available in your country.