I think your "network" statement is in error.  Try adding either of these statements (or both?) into BGP's IPv4 address family:

network 192.168.0.0 mask 255.255.255.252

network 192.168.0.16 mask 255.255.255.248

The network statement only populates prefixes into the routers BGP database, if that prefix exists in the router's routing table.  You don't have 192.168.0.0/16 in your routing table (according to PacketTracer's display, anyway), so the network statement isn't putting anything into BGP.

Note, BGP almost always requires a route-map to work the way you want it to work.  If you want to only advertise the summary address and not the more-specific prefixes, you need to apply a route-map on the neighbor relationship.  If you're ok with the ISPs learning the more-specific addresses also, then knock yourself out.

Alternately:

You can add a static route to interface null0.  This is known as black-hole routing, and doing this on the summary address makes that static route an "anchor route."  If you add that static route, then 192.168.0.0/16 gets populated into the router's routing table, and the network statement puts the summary address into the BGP database.  In this case, you also don't need the aggregate-address command.  Note that the more-specific routes will always win, even over a static route.

weylin