I tried to substitute all +'s with an escaped plus but that didn't work. It just substitutes with another '+'(the backslash apparently doesn't show in the string).

If this is the case, your substitution code probably looked something like s/\+/\+/g which is incorrect, you're escaping the + on the rhs not adding a backslash, you would need to do s/\+/\\+/g, but don't do that either, if you want to escape metacharacters use quotemeta() or \Q