Flybe just cancelled my return flight. Will they refund that part of the trip?

Yesterday I received an email from Flybe that my return flight in January has been cancelled. They said that I need to book another ticket and they will refund. But I'm not clear about how much would it be.
The ticket I bought is from SOU (Southampton) to AGP (Malaga) and return.. Now I have to find alternatives for the return and I found from AGP (Malaga) to LGW (Gatwick) which far (2 hours by train from Southampton).
The original ticket I paid was £410 (2 adults & 1 baby). now for the return to Gatwick I found it for £100.. (Plus I need to buy train tickets). What I paid for the return flight is roughly £190. so if the refund me only £100 they will still owe me £90.
I know calling can help.. the problem is that every time I called is 30 minutes waiting to be answered. So I want to know my options.
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Can I get a refund if part of my flight is Cancelled?
You can get your money back for any part of the ticket you haven't used. So if you booked a return flight and the outbound leg is cancelled, you can get the full cost of the return ticket refunded. If you still want to travel, your airline must find you an alternative flight.What happens if part of your flight is Cancelled?
If your flight is canceled by the airline, you will either be accommodated on a later flight or, if you decide not to travel, you are entitled to a full refund under federal law. If the flight had multiple stops, you would be refunded for the unused portion of the flight.Airline Refunds - Flight Cancelled? Know Your Rights!
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