The most convenient way to buy cryptocurrency is to use an exchange. But you will need broker support
You can use the BestChange service. On 2007 Exchange monitoring BestChange was launched, and still continues improving everyday. There are over 440 exchangers on the BestChange website. Every exchanger present has been thoroughly checked before listing, and BestChange team constantly monitors due performance of exchangers.
Here you can find an exchanger for converting dogecoin to usd https://www.bestchange.com/dogecoin-to-visa-mastercard-usd.html or any other cryptocurrency pair