MWEB account cancellation, or lack thereof.

Have been an MWEB client for some years now. I have been trying to check my data usage as my monthly invoice has jumped 70% since mid 2019, so want to check why. I have logged in to my account, but all I get is a remark : Aw, there seems to be a problem. I now want to cancel my month-month G3 subscription, but this seems impossible to do on the website. Under the Products tab, the first line says you can cancel on this page, but there is nothing about cancellation here! Tried sending a query, and using drop-down selectors, indicated I wanted to cancel my subscription, which then brings up a 'click here' button to cancel, but it only directs you back to the Products page where there is no cancel feature. Totally frustrated, meanwhile they will keep taking from my debit order ! Any advise from anyone ? Otherwise, will have to go to their office and try cancelling in front of them.