i can't backup my phone via icloud due to lack of space and neither by pc due to an arror occuring. what can i do to back up my phone thanks

Hi

just been to apple store as i am having trouble

1) updating new software

2) icloud wont back up phone due to lack of storage

3) I can't but extra icloud space due to the fact the phone is a replacement and itunes cant verify the bank details

4) when i try to backup to pc it says itunes could not back up i phone - becasue the backup was corrupt or not compatible with the iphone

Not sure what else to try

Please help ... many thanks