Its impossible to tell whether or not you are getting good value on the basis of the information you provide.
It is meaningless to compare your fee this year to your fee 2 years ago if the work involved in both scenarios is different.
You say that the second fee includes work covering 2 tax years, unless this was also the case first time around there will obviously be additional work & cost this time around. In addition, registration for self-assessment will invariably mean that your tax affairs are more complicated than previously.
In general, the ever increasing burden of regulation of accountants (eg the recent 'Anti Money Laundering' regulations and the forthcoming 'Financing of Terrorism' regulations) tend to push up accountancy fees due to the volume of additional work necessitated. Every accountant is obliged to operate full client ID verification and other anti-money laundering procedures on each & every client, even, bizarrely, straightforward PAYE tax return cases.
It is also impossible to judge the "defamation" issue without seeing the exact text of your letter to him. He is entitled to protect his good name if you did defame him - please note that I'm not saying that you did - but if you are satisfied that your comments were correct and are capable of being substantiated, you should not worry unduly about this particular issue.