Check the datatype of mobileno field.

Error: ORA 1722
Text: invalid number
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Cause: The attempted conversion of a character string to a number failed
because the character string was not a valid numeric literal. Only
numeric fields or character fields containing numeric data may be used
in arithmetic functions or expressions. Only numeric fields may be
added to or subtracted from dates.
Action: Check the character strings in the function or expression. Check that
they contain only numbers, a sign, a decimal point, and the character
"E" or "e" and retry the operation.