How to correctly pass filterexpression through SOAP

Hi, all.

I am trying to pass the FilterExpression object to my custom service.
The Request:
<soapenv:Envelope xmlns:soapenv="schemas.xmlsoap.org/.../envelope" xmlns:tem="http://tempuri.org/" xmlns:con="schemas.microsoft.com/.../Contracts" xmlns:arr="schemas.microsoft.com/.../Arrays" xmlns:xsi="www.w3.org/.../XMLSchema-instance" xmlns:q1="schemas.microsoft.com/.../Query">

<soapenv:Header/>
<soapenv:Body>
<tem:QueryData>
<!--Optional:-->
<tem:qe>
<!--Optional:-->
<con:ColumnSet>
<!--Optional:-->
<con:AllColumns>true</con:AllColumns>
</con:ColumnSet>
<!--Optional:-->
<con:Criteria>
<con:FilterOperator>And</con:FilterOperator>
<!--Optional:-->
<con:Filters>
<!--Zero or more repetitions:-->
<con:FilterExpression>
<con:Conditions>
<con:ConditionExpression>
<con:AttributeName>createdon</con:AttributeName>
<con:Operator>GreaterEqual</con:Operator>
<con:Values>
<con:Value xsi:type="xsd:string">2015-12-01</con:Value>
</con:Values>
</con:ConditionExpression>
</con:Conditions>
</con:FilterExpression>
</con:Filters>
<!--Optional:-->
</con:Criteria>
<con:EntityName>contact</con:EntityName>
<!--Optional:-->
</tem:qe>
<!--Optional:-->
<tem:Login>login</tem:Login>
<!--Optional:-->
<tem:Password>password</tem:Password>
<!--Optional:-->
<tem:Domain>domain</tem:Domain>
</tem:QueryData>
</soapenv:Body>
</soapenv:Envelope>

And I am getting an error in Response:

<Message>The ConditonOperator.GreaterEqual requires 1 value/s, not 0. Parameter Name: CreatedOn</Message>

How can I correctly pass the values collection element?

Thank you. With regards, Yuriy.