Try with this code part:
client.println(F("POST /WebServiceSQL/WebServiceSQL.asmx HTTP/1.1"));
client.println(F("Host: 192.168.2.90"));
client.println(F("Content-Type: text/xml; charset=utf-8"));
client.println(F("Content-Length: 350"));
client.println(F("Connection: close"));
client.println(F("SOAPAction: \"http://toponet.zapto.org/logactivation\""));
client.println();
client.println(F("<?xml version=\"1.0\" encoding=\"utf-8\"?>"));
client.println(F("<soap:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\">"));
client.println(F("<soap:Body>"));
client.println(F("<logactivation xmlns=\"http://toponet.zapto.org\">"));
client.println(F("<pinnumber>3</pinnumber>"));
client.println(F("</logactivation>"));
client.println(F("</soap:Body>"));
client.println(F("</soap:Envelope>"));
You escaped several numbers unnecessarily in the header. You also moved a header line to the end of the request which isn't allowed. You XML wasn't valid (attributes must be double quoted) and quoting the integer isn't necessary. The value of the content length header must match the actual body size. I probably found the most obvious errors, maybe there are more.
You should read about the basics in HTTP and XML, probably also about WebServices before trying to implement such a call in an embedded platform.