She's talking about the weight limit of the car seat, not the weight of the baby.
OP at 9 months you need a bigger rear facing seat :)
You could choose something that spins, has the option to forward face later if you want to (from 15 months minimum; it's safer to rear face as long as possible) and lasts until around age 4. Popular options here are Britax Dualfix, Cybex Sirona, Joie 360 Spin or Maxi Cosi Mica. They will only last until age 4 if your baby is average size.
Or you could choose something which is only rear facing, but lasts much longer, more like up to age 7 (less if your child is tall for age). These are a good choice if you have a baby on the bigger side or if you just want to rear face as long as possible/get the safest seat possible. Good options here are Britax Max Way Plus or Axkid Minikid.
If your baby is on the smaller side for their age and is not yet sitting up then you will need one that is suitable from a slightly younger age. The spinning up to age 4 seats work well here, or if you want the longer lasting + extra safety, Besafe Stretch is a good option.
I would not personally recommend the seats that go up to age 12; they tend to be a bit of a false economy and they don't perform that well for safety because they combine too many features into one seat.
You can also continue to use the seat that you have until your baby's head is at the top of the shell if you want to. Legs over the end doesn't matter. Make sure that you move the straps up to the larger settings, don't leave them on the newborn setting. If it's the i-Snug seat that you have, it is also outgrown at 75cm even if the baby's head isn't yet at the edge.