@kokobi, add-on purchase is a two step process as illustrated in the link below. Please check the self serve to ensure both steps have been completed successfully.
https://productioncommunity.publicmobile.ca/t5/Plans-Add-Ons/HOWTO-Purchasing-Add-ons/m-p/198974
If there continues to be issues with using the data, please check the phone to ensure mobile data is turned on and that any data usage limits if set have not been exceeded. Check also APN settings to ensure they are correct.
Refer to the following knowledge base link of setting up the APN.
APN Settings:
Name: Public Mobile
APN: sp.mb.com
Proxy: Not set
Port: Not set
Username: Not set
Password: Not set
Server: Not set
MMSC: http://aliasredirect.net/proxy/mb/mmsc
MMS proxy: 74.49.0.18
MMS port: 80
MCC: 302
MNC: 220
Authentication type: Not set
APN type: default,mms,supl
APN protocol: IPv4
APN roaming protocol: IPv4
