You need to get them to tell you in writing HOW a ticket can be cancelled - I've posted a link to their website above which shows that the passenger cannot cancel tickets. Therefore, the onus is on them to prove that it was you - given that there is no mechanism available to you to cancel tickets.
As regards the delay in hearing back, you may not have heard that Ryanair is currently experiencing the biggest customer-service cock-up in its history, having had to cancelled over 2000 flights in the next 6 weeks due to staff shortages and rostering problems, thereby disrupting the travel plans of hundreds of thousands of passengers. They are incredibly busy at the moment dealing with complaints, compensation claims, etc.
But stick at it.