The Bulgarian Migration Directorate misapplies the Directive 2004/38/EC of the European Parliament. The Directive regulates the regime of free movement of EU citizens and members of their families.
The particular rule that has been misapplied is that the citizens of EU member states are under the same regime as the members of their family in other EU host country. The only difference is that, in some EU member states, the family members may be required to apply for entrance visa. NO other requirements are set in the directive.
If you are married to a Bulgarian (already a EU citizen), you can apply for long term residence, on the ground that your spouse is a Bulgarian. The Migration Directorate will issue a long term certificate for you, but it will require you to pay 500 Levs per year.
Usually, the latter fee is required by the common foreigner regime. The fee is not required for family members of EU citizens. But Bulgarians are EU citizens, aren't they?
A paradox! You are eligible to receive residence certificate on the ground of EU Directive, but you have to pay a fee which is required by the common regime. In fact this fee should be illegal.