I am wondering if I can keep paying on the phone monthly, but disconnect other data fee. My son is not able to have his phone back until April so I am paying for a plan he doesn't use and hasn't used since November.
Your best bet is to put it on 'vacation disconnect'. It will fully disable the phone but you get to keep the number. You can do this onnline at the koodo self serve site. It's $15 a month. One thing is that the plan he is currently on, he may not be able to get back on if by the time you give the phone back to your son the plan is not available from koood. The disconnect can be done for a max of 6 months.
You could also consider porting his # over to prepaid, that way you can only allow him to text and make evenings/weekends calls. You can simply not add any data boosters. This will require you to pay out any negative Tab balance, however.
I guess depending on the tab balance you can always cancel the account get billed out for it and reactivate if you wish not to pay the monthly fees. Keep in mind, the # will be lost if you wish to go this route.