It is very sad that you’re having to retire your well-maintained Polo due to the 15-year rule in Delhi NCR. Since you have a budget of Rs 7 lakhs, we’d advise you to get a 2020-21 Maruti Brezza or Toyota Urban Cruiser, both of which are smooth, well-built cars. Their seating position is high, visibility is good, and controls are light, which makes them very user-friendly.
Also, try finding the newest possible example, which will ensure that you drive the vehicle for 9 or 10 years before it reaches the 15-year age-limit.
For your outgoing car, you could consider getting in touch with used-car platforms such as Spinny; they’ll do the paperwork, and should get you a good price.