Mark

My comments are based on the corrections you received.

乘坐 （cheng2 zuo4)

乘 (cheng2)

坐 (zuo)

are used to ride a bus, a train or plane to some location and they are placed after the subject, except if the verb is an auxillary verb like 想， 可以， 能， 等。。。Those words are all interchangable ...

乘坐 （cheng2 zuo4)
乘 (cheng2)
坐 (zuo)

+ noun = prepositions phrase and prepositional phrases appear before verbs in Mandarin.

This applies to the correction 在车里 as well, since this is also a prepositional phrase ... if you want to know if a phrase is a prepositional phrase, ask yourself, does the verb happen at the location? if so, then, in Chinese, in order to complete the action of buying a transportation card, the person must first arrive at the transportation station, hence this phrase is said/written first.

Chinese sentence order:
Person at some time at some location do what thing ... if the action (verb) happens after a person goes to the location, then the location comes first ... if the verb (action is completed) before the subject arrives at the location, then the verb comes first. 

想到 was probably changed because 到 suggestion that the process of thinking is complete ... and based on the context of the dialog, the person has not truly settled his thoughts on the matter since he is still asking questions and doubting. I'm not a 100% sure if I'm correct on this one ...

想到 also means to recall something. 

交通卡

:::我想坐公交车 我可以在车里买公交卡吗？

不可以 所有的公交车站都有卖卡的售货机

:::我可以用信用卡吗

我不知道 我想你必须用现金

我不清楚你是在什么语境下的对话，只能按我猜想的意思完成对话，

在中国坐车一般是刷卡或者用零钱，在公交车站是可以办卡的，但是我不确定每个地方都有卖卡的售货机，你指的是自动售票机吗？

交通卡

:::我想上公交车去 我可以在车里面买交通卡吗？ 

不可以 所有的公车站都有卖卡的售货机

:::我可以用信用卡吗

我不知道 想到必须用现金

交通卡

:::我想上公交车去 我可以买交通卡在车里面吗？

－》我想乘坐公交车，我可以在车里买交通卡吗？

不可以 所有的公车站有卖卡的售货机
－》不可以在车里买交通卡，但是可以在公车站买交通卡。

:::我可以用信用卡马
－》我可以用信用卡吗？

我不知道 想到必须用现金

－》我不知道，但我想应该要用现金吧。