Serious problems with Momemtum

I have been trying to cancel my service with momentum since 25 November largely because of their failure to pay for my covid test as per previous complaint on HP and and they keep stalling or finding a reason to not get back to me. I sent an email on 25 November - Then on 1 December they asked for my membership number even though my ID was right below my name. Then on Then again on 1 December - Then I phoned on 3 December. I am still waiting for confirmation that that December is my last month with them