Unless it’s changed, I believe the limit is 7. This will vary though depending on many factors such as your credit class.

Could you share a screenshot of exactly what the error message says?

Looks like you can't add any more subscribers to your account.

have been with them since 13 years and have never had an issue with non payment it comes auto pay off my credit card 

Let me flag a rep and see if they can provide any more insight or if the limit has changed.

Hi @shauna0518 

Normally, the max limit is 7 lines, however it depends on multiple factors, such as the payment history, the tenure of the account.

Have you tried adding a new line on a different browser or using the private mode on your browser?

Are you getting the same message?

I will try that Thank you

What is your elderly mother's phone usage like? If she just need a basic plan such as unlimited Canada wide calls and texts, you should check out public mobile or prepaid service. 

I set up an account for my elderly MIL with public mobile and managing her account. You can check her usage and you can add data if you need. It's easy and cheaper than adding her under my account.

Separate Prepaid account for youngsters and elderly is a good idea. No danger of accidental long distance, overages, Easy Roam or purchases being added to your phone bill.