No Cash back benefit

I have been fighting with Vitality to get my cash back since January this year. All they have to say is that my MySchool card is not linked to Vitality. It has always been linked because I used to receive my cash back benefit. It suddenly stopped working.

I asked the MySchool card section, as far as they know it has always been linked.

I'm tired of these non-ending useless emails. Can I cancel my Vitality subscription in the middle of the year?