Solicitor’s retention of client records

I asked my solicitor for a copy of all documents relating to a case they worked for me in mid 2015.

The solicitor, after several weeks of not replying to emails or phone calls, has claimed they no longer have the files. Aren’t solicitors under a legal obligation to store client files for a min for 6 years? The solicitor claimed they needed to keep the files for a reasonable period of time, which has now elapsed and the files were disposed of accordingly.